diff --git a/AHT20_sensor_control/AHT20_sensor_wrapper.py b/AHT20_sensor_control/AHT20_sensor_wrapper.py
index 6ef5747..d2cba50 100644
--- a/AHT20_sensor_control/AHT20_sensor_wrapper.py
+++ b/AHT20_sensor_control/AHT20_sensor_wrapper.py
@@ -194,9 +194,9 @@ def CheckCRC(self):
         """
         # Get all 6 bytes data and 1 bytes CRC code
         frame_for_CRC8_check = 0x00
-        for i in range(0, 7):
-            frame_for_CRC8_check << 8 | self.all_data[i]
-        isCRCOK = AHT20_crc8_check(frame_for_CRC8_check)
+        # for i in range(0, 7):
+        #     frame_for_CRC8_check << 8 | self.all_data[i]
+        isCRCOK = AHT20_crc8_check(self.all_data)
         if (isCRCOK):
             return AHT20Status.AHT20_CRCOK
         else:
diff --git a/AHT20_sensor_control/crc8_helper.py b/AHT20_sensor_control/crc8_helper.py
index 79b57cc..6543e66 100644
--- a/AHT20_sensor_control/crc8_helper.py
+++ b/AHT20_sensor_control/crc8_helper.py
@@ -1,6 +1,92 @@
+# Usage: AHT20 crc8 checker. 
+# A total of 6 * 8 bits data need to check. G(x) = x8 + x5 + x4 + 1 -> 0x131(0x31), Initial value = 0xFF. No XOROUT. 
+# Author: XU Zifeng. 
+# Email: zifeng.xu@foxmail.com
+N_DATA = 6
+# 1 * 8 bits CRC
+N_CRC = 1
+# Initial value. Equal to bit negation the first data (status of AHT20)
+INIT = 0xFF
+# Useful value to help calculate
+LAST_8_bit = 0xFF
 
-def AHT20_crc8_check(int_data):
-    pass
 
-def AHT20_crc_calculate(int_data):
-    pass
\ No newline at end of file
+# Devide number retrieve from CRC-8 MAXIM G(x) = x8 + x5 + x4 + 1
+CRC_DEVIDE_NUMBER = 0x131
+
+# Data and CRC taken from AHT20, use this for testing?
+TEST_DATA = [[28, 184, 245, 165, 156, 208, 163], [28, 185, 16, 149, 156, 83, 112], [
+    28, 184, 249, 85, 156, 114, 213], [28, 185, 9, 53, 156, 54, 45], [28, 185, 70, 117, 156, 189, 33], [28, 185, 64, 165, 156, 61, 209]]
+
+
+def mod2_division_8bits(a, b, number_of_bytes, init_value):
+    "calculate mod2 division in 8 bits. a mod b. init_value is for crc8 init value."
+    head_of_a = 0x80
+    # Processiong a
+    a = a << 8
+    # Preprocessing head_of_a
+    for i in range(0, number_of_bytes):
+        head_of_a = head_of_a << 8
+        b = b << 8
+        init_value = init_value << 8
+    a = a ^ init_value
+    while (head_of_a > 0x80):
+        # Find a 1
+        if (head_of_a & a):
+            head_of_a = head_of_a >> 1
+            b = b >> 1
+            a = a ^ b
+        else:
+            head_of_a = head_of_a >> 1
+            b = b >> 1
+        print("a:{0}\thead of a:{1}\tb:{2}".format(
+            bin(a), bin(head_of_a), bin(b)))
+    return a
+
+
+def AHT20_crc8_calculate(all_data_int):
+    init_value = INIT
+    # Preprocess all the data and CRCCode from AHT20
+    data_from_AHT20 = 0x00
+    # Preprocessing the first data (status)
+    # print(bin(data_from_AHT20))
+    for i_data in range(0, len(all_data_int)):
+        data_from_AHT20 = (data_from_AHT20 << 8) | all_data_int[i_data]
+    # print(bin(data_from_AHT20))
+    mod_value = mod2_division_8bits(
+        data_from_AHT20, CRC_DEVIDE_NUMBER, len(all_data_int), init_value)
+    # print(mod_value)
+    return mod_value
+
+
+def AHT20_crc8_check(all_data_int):
+    """
+    The input data shoule be:
+    Status Humidity0 Humidity1 Humidity2|Temperature0 Temperature1 Temperature2 CRCCode.
+    In python's int64.
+    """
+    mod_value = AHT20_crc8_calculate(all_data_int[:-1])
+    if (mod_value == all_data_int[-1]):
+        return True
+    else:
+        return False
+
+
+
+def CRC8_check(all_data_int, init_value=0x00):
+    divider = 0x107
+    DATA_FOR_CHECK = all_data_int[0]
+    for data in all_data_int[1:-1]:
+        DATA_FOR_CHECK = (DATA_FOR_CHECK << 8) | data
+    remainder = mod2_division_8bits(
+        DATA_FOR_CHECK, divider, len(all_data_int) - 1, init_value)
+    if (remainder == all_data_int[-1]):
+        return True
+    else:
+        return False
+
+
+if __name__ == "__main__":
+    print(CRC8_check([0x66, 0x44, 0x33, 0x22, 0x24], 0))
+    for data in TEST_DATA:
+        print(AHT20_crc8_check(data))