The invention relates to a key exchange method for automobile electronic control unit communication, which comprises the following steps that 1, an encryption object is selected, and a plurality of electronic control units are classified into a Master and a Slave; 2, a system is initialized, the Slave is accessed to the Master, and the Master checks whether a key parameter needs to be generated ornot; if so, a key parameter is generated, and simultaneously the key parameter is stored into safe storage areas of the Master and the Slave; if not, the originally generated key parameters are used;3, a secret key is generated in real time, after the vehicle is ignited each time, the Master and the Slave respectively generate a random number, and the secret key is generated according to secretkey parameters and the random numbers; and step 4, data encryption: the Master encrypts the communication data needing to be sent to the Slave through the secret key, and the Slave encrypts the communication data needing to be sent to the Master through the secret key. The secret key exchange method for automobile electronic control unit communication is low in encryption cost, does not need to establish a special server to store the secret key, is low in secret key leakage risk, and has very high safety.