Abstract: Aluminum alloy terminal connectors for substation in a power company occurred batch cracking during operation. The cracking causes and mechanisms of terminal connector were analyzed by means of macro observation, fracture analysis, chemical composition analysis, mechanical property test and freezing simulation test. The results show that there were weld defects in weld seam of terminal connector, which decreased the strength of weld. There was cavity at the bottom of connecting tube of terminal connector, the accumulated water in connecting tube frozen and expanded in cold weather, which made the weld seam cracking under the load beyond design condition, and caused the cracking of terminal connector.