If the location of CAN bus “carrier listening sampling point” is not set properly, it may affect the reliability of network data transmission in harsh electromagnetic environment. To measure the exact location of the sampling point, an error injection method is studied. This method is based on the error detection mechanism and the principles of CAN bus protocol, and the recommended range and value of sampling points in aviation and automobile industry standards. With this method, the principles of selecting test area is analyzed, a special test device has been developed and a verification test has been carried out. The device is used to test the sampling points of a certain type of CAN bus equipment, and the test results are analyzed under characteristic load conditions. This method realizes the high precision measurement of the location of CAN bus carrier listening sampling point, provides measurement support for improving the reliability of CAN bus network, and provides data base for reducing the tolerance of sampling points in the network.