The finite element analysis method is widely used in the field of transformer design and insulation optimization. This study is based on the finite element method and constructs a Tesla transformer calculation model for electric field distribution calculation. On this basis, electrostatic analysis and insulation optimization work of Tesla transformer with a working voltage of 1.2 MV are carried out. The results indicate that adopting the method of bonding the inner conductor and supporting insulator surface of Tesla transformer can effectively optimize the electric field distribution inside Tesla transformer. Based on this, this study designs an insulator structure for inner conductor support. The overall field strength level of the optimized Tesla transformer is about 118 kV/cm, and the highest field strength level of local insulators is about 162 kV/cm. The overall insulation level of the Tesla transformer meets safety requirements. The research results of this study can provide reference for the calculation of electric field distribution and insulation design of tesla transformers with a working voltage of MV level.