A stochastic unit commitment（SUC） method is presented， considering conventional thermal units， flexible generating units and wind turbines aimed at energy saving and environment protection. The flexible generating unit has various operation modes. Each operation mode is modeled as a pseudo unit and the switch between two modes is implemented by setting some constraints. Therefore they are easy to be combined with the conventional unit commitment（UC） method. The UC risk constraints are developed and combined into the model. The demand fluctuation， the unit force outage， even the stochastic characteristic of wind generation can be dealt with by different forms of UC risk constraints. Numerical simulations on two simple test systems show that the presented SUC method is effective to schedule flexible generating units and deal with their stochastic characteristics. The results of four test systems with different scales show that the calculation time of the method is acceptable and practical.