Abstract: When the engine was inspected on the ground, a crack was found in the intake pipe connected to the engine. In order to determine the cracking mode and mechanism, macro and micro examination on the cracking site was carried out, and ANSYS software was used to simulate the static state and mode so as to analyze the working state of the pipe. The results show that the weld position at the branch ear cracked due to abnormal external force or stress concentration, and the crack propagated under vibration conditions.