This article presented the comparisons of two different testing methods and different curing conditions for heat deflection temperature（HDT）. The effects of curing condition, curing agent, diluent and toughener on the heat resistance performance of epoxy structural adhesive were studied by testing the HDT of epoxy structural adhesives, and an optimized formula of pressure injection adhesive for steel-bonding was found. The results have indicated that epoxy structural adhesive has good heat resistance performance and impact toughness by using rigid curing agent (such as modified alicyclic amines and phenolic amine), epoxy diluent with high functionality and the “island structure" toughener. The optimized adhesive has a HDT up to 65.9 ℃ and a T impact peeling length of 21mm , whose overall performance can meet all the requirements of structural strengthening.