Abstract: Stress relaxation is considered to be one of the main factors causing the increase of contact resistance of crimping fittings for transmission lines. It is very important to study the effect of stress relaxation on the contact resistance of crimping fittings for evaluating the quality and health of crimping fittings. Through conducting the cyclic current test of crimping fittings,the influence of stress relaxation caused by the cyclic current on contact resistance of bad crimping fittings and good crimping fittings was compared. The difference between temperature rise of joints and contact resistance in evaluating crimping quality was studied,and the application of on-line measurement of contact resistance in engineering was discussed.