To study the effect of hydrodynamic performance on the new type vertical axis tidal turbine, using ANSYS-CFX software is adopted to simulate different working conditions for comparing the hydrodynamic performance between cross-type twin-turbine and H-type single turbine. Cross-type vertical axis tidal current twin-turbine is an improved form to traditional H-type turbine. The results show that: the efficiency of twin-turbine is about 10% higher than that of single turbine. The efficiency of twin-turbine changes little for ebbs and flows. The average values of thrust, lateral force and moment are equal between cross-type turbine and H-type turbine, but cross-type turbine's amplitude of fluctation is far less than that of H-type turbine, which can produce beneficial effects on the structure safety and fatigue life of turbines. Therefore, the cross-type vertical axis tidal current twin-turbine has obvious advantages compared to H-type single turbine in the efficiency and guarantying running life.