This paper discusses a new distribution operation mode based on distribution system security region（DSSR）theory for smart distribution grids.Firstly，the effects of total supply capability（TSC）and DSSR of a smart distribution grid are analyzed.Using the TSC theory，the efficiency of a distribution network can be significantly improved under the N-1 security principle.The DSSR theory enables the real-time security assessment.Secondly，a security framework is introduced for distribution networks;the classification of power system states and self-healing control are defined as well.Then，the method of self-healing control is extended based on DSSR and TSC.Thirdly，a new self-healing control system is introduced for smart distribution grid operation.This system consists of functions such as monitoring，alarming，control，optimization，risk evaluation and so on.The new distribution operation mode is also compared with the operation mode with distribution automation and the transmission operation methods.Finally，a real medium-voltage distribution system is presented to prove the proposed security control method.The results show that the self-healing control system can be used to achieve a more secure and efficient smart distribution system.