Under the electricity market environment， the minimum total cost model of the distribution company is presented. Several issues， such as distributed generation（DG） and the cost of the curtailed load， are involved in this model. Three modes， i.e.， tradition mode， intentional islanding mode and non-fault feeder sustaining mode， are compared. In the case of fault occurred under different load level， there modes are analyzed in three areas， i.e.， the distribution system loss， the node marginal price and the distribution company's total cost. Numerical tests show that the intentional islanding mode can reduce curtailed load and decrease the power purchasing cost of the distribution company. It also indicates that the distribution company can choose the optimal sustaining mode according capacity margin of non-fault feeders.