In this study, the mechanical properties and damage modes of pultruded glass fiber/unsaturated polyester composite square pipe for automotive parts were investigated. The pipe structure, fiber mass content, dynamic mechanical analysis, tensile, and bending properties and acoustic emission detection damage mechanism of pultruded glass fiber composite pipe were studied. The structure of the cross‐section of the pultrusion pipe is like a sandwich composed of mat layers on both surfaces and a unidirectional fiber layer in middle. Based on the failure analysis of pipe by acoustic emission signal technology, it is found that the tensile damage process was considered into four stages, initial damage, mat layer fracture, intermediate damage, and fiber fracture; while the bending damage process can be divided into two stages as initial and overall damages.