In the process of two-pass micro plasma arc welding of titanium alloy sheet,based on the thermal contact resistance theory,a three-dimensional transient heat transfer finite element model of contact heat transfer between titanium alloy sheet and flexible fixture was established.The effects of contact upper surface temperature,micro-contact thermal resistance,micro-gap thermal resistance,DC and pulse welding on thermal contact resistance were investigated,and the simulation and experimental results were compared.The results show that the thermal contact resistance increases as the temperature increases when the temperature of the contact upper surface (titanium alloy sheet) is in the range of 290-350 K.The effect of micro-contact thermal resistance on the thermal contact resistance is 26.1％-46.3％ larger than the micro-gap thermal resistance.The thermal contact resistance of pulse welding is 3.1％-3.5％ larger than DC welding.The error of simulation and experimental results of weld pool depth is 8.6％,which verifies the reliability of the model.