To deal with the large scale unit commitment problems， a new linear mixed integer programming algorithm based on dynamic search technology is proposed. Based on the framework of branch linear mixed integer programming， a new concept， dynamic search， is introduced in this approach. To cut the branches， the constraints concerning time and power are considered separately. For different systems， time of calculations as well as precision of result can be adjusted with appropriate parameters. The result of the test system shows that the presented algorithm is fast， accurate and especially suitable for the unit commitment of large scale power systems.