In order to adapt the new situation that large-scale wind power is being integrated into power system more and more, the probabilistic production simulation method for mixed windhydro-thermal power system is researched and improved in this paper. The units loading order is redefined based on equivalent continuous load curve. The indices of loss of wind energy expectation (LWEE) and abandoned wind rate (AWR) are proposed based on the improved production simulation. The analytical expression of partial derivative of the indices with respect to conventional unit capacity is derived based on cumulant method. The results on IEEE-RTS79 system demonstrate that the proposed method is feasible and effective.