The simulation of transverse field sweeping system (TFSS) for a 170 GHz, MW-class gyrotron with single-stage depressed collector (SDC) is presented in this paper. The adoption of SDC aims to recover part residual kinetic energy of spent electrons as well as to improve total efficiency exceeding 55%. Transverse field sweeping system is coming into use to expand the spent electron trajectory length to 1100 mm to keep the specific heat dissipation on the collector surface within technically acceptable limits. Furthermore the modulation depth of sweeping signal and the number of transverse coils are simulated to get an optimal result 38.9% and 6 leading to an acceptable peak averaged power density . In order to ensure the safety and feasibility in actual situation, the cooling system with axial groves for collector is also designed and the thermal and fluid analysis are carried out by commercial available software ANSYS. The maximum temperature of inner and outer collector surface are and respectively. The range of water temperature at the inlet and outlet are and respectively.