An analysis is made of the power system self-organized criticality using the complexity theory， and the power law relationship between the cascading scale and the corresponding frequency is verified on the basis of a DC power flow model. The control rule is incorporated in the DC power flow model， whose target is to reduce the expectation of the cascading scale. And a new power law function is obtained in long-time simulation. It has been found that， compared with the power law function from the DC power flow model without imposed rules， the slope of the new power law is increased in log-log coordinates， which is tantamount to an improvement in the distribution of fault temporal series. So the incorporation of correct control rules can prevent large-scale outage of power system and reduce the fault expectation scale.