Efficient extraction of minimal siphons is fundamentally important in deadlock control. So far, methods that are based on problem reduction and decomposition are recognized as effective ways. In this paper, an improved method is proposed to identify all minimal siphons. New conditions are proposed under which a problem needs not be decomposed. It significantly simplifies the process of problem decomposition in the existing methods, thereby reducing the memory and improving the computational efficiency. An example is used to illustrate the application of the proposed method.