Abstract: To solve the problems of small startup moment and long startup time of the H-type hydrokinetic rotor, the simulation and analysis were conducted by the computational fluid dynamics method. The six degree of freedom（6 DOF） method was adopted to model the variation of rotational speed of rotor with the torques acting on rotor. Comparison and correlation analysis were conducted among transient flows, rotational speed and output torque at different initial setting angles. The results show that there is no explicit correlation between rotational speed and output torque during the startup process of the vertical shaft hydrodynamic rotor with straight blade. As the rotor starts up at the minimum static torque, the time required to reach the maximum rotational speed and output torque is longer than that associated with the maximum static torque. As the maximum rotational speed is attained, low-pressure zones are produced in the area enclosed by the blades, which is insensitive to the initial setting angle. Large area of low-pressure zones is responsible for low output torque. As the rotor starts up at the maximum static torque, the integrity of the wake flow is relatively high. The rotational speed experiences increasing, decreasing and subsequent regular oscillation, which is common at different chord lengths of the airfoil. As the chord length is increased from 0.16 m to 0.24 m, the startup time is extended by 0.63 s, and the average rotational speed is decreased for the stabilized rotation, but the fluctuation amplitudes remain nearly invariant.