The Darrieus VAWT has been considered by many scientists due to the simplicity of design and independence to the wind direction. The straight-bladed Darrieus wind turbines have the inherent problem of self-starting inability. In this study has been showed that use of the variable pitch angle blades is a suitable solution to overcome the self-starting problem and increasing the output power. So, the effect of variable blade pitch angle mechanism on output torque, flow field around the rotor and self-starting of Darrieus wind turbine has been investigated. The unsteady two-dimensional simulation is conducted using computational fluid dynamics withSST k? turbulence model and moving mesh technique is used for simulation of the rotating rotor. The numerical investigation shows that variable pitch mechanism decreases the angle of attack makes the turbine have a chance to produce more torque at different azimuthal angles. Also the use of variable pitch blades increases the pressure difference between the low and high pressure of around the blade and delays stall. So, the Darrieus turbine with variable pitch angle in comparison with zero fixed pitch angle blade Darrieus turbine has the ability to produce more power at the middle and lower tip speeds ratios.