This paper presents a new approach to minimize the operation cost of wind-diesel system. Under the constraints of diesel units＇ startup/shut down time, ramp rate and power balance etc., the ＇Unit Commitment＇ concept is introduced to construct the model for optimal operation planning of all the diesel units. Dynamic programming (DP)method is applied to solve the problem. A test system is used to demonstrate the features of our proposed method and some interesting results are reached.