Orthogonal test is used to optimize the resistance spot welding parameters of Q345 D carbon steel. Through single factor analysis of welding current,welding time and electrode pressure which have great influence on spot welding strength,the rule of influence of welding parameters on tensile strength of spot welding is obtained,and the procedure window of spot welding parameters is gained. On the basis of single factor analysis, three factors and three levels orthogonal test parameters are determined to conduct spot welding experiments. The range and variance analysis of the orthogonal test results are carried out by using the tensile strength of spot welding as the evaluation index. The optimum parameters of Q345 D spot welding are gained as follows: welding time of 25 CYC,welding current of 12 kA and electrode pressure of 7.5 kN.