A finite vortex method was developed based on the Kutta condition of pressure difference at the trailing edge of an airfoil aiming at the analysis and prediction of hydrodynamic load and wake field of cycloidal vertical axis tidal turbine. The empirical value of the trailing edge pressure difference parameter was obtained by comparing with the experimental value of static lift coefficient of NACA0015 airfoil. The instantaneous and average loads of fixed pitch turbine and cycloidal turbine with different eccentricity are compared. The results show that the positive torque of the turbine is mainly concentrated in the upstream area of the actuator disk. Cycloidal turbine can not only improve the power coefficient, but also reduce the force's amplitude of the blade. By comparing the structure and evolution process of turbine wake, the sources of the trailing vortex in the upper and lower regions are found. They are obtained from the starting vortex and the vortex flipped off by the blades, respectively. The wake of a turbine with high power coefficient develops more rapidly downstream.