A mixed-integer nonlinear programming model is developed for reducing excessive standing phase angle difference across open circuit breakers in transmission loop paralleling operation. The model adopts the active power and input load as control variables while taking the importance of the to-be-restored load into account. The minimum number of participating generators is determined based on the dichotomy theorem. Then the optimal control algorithm for standing phase angle reduction in power system restoration is developed. The method asks for fewer participating generators and less active power adjustment. The condition for transmission loop paralleling operation can be reached in a shorter time. Meanwhile， part of the important load can be restored. Simulation results of New England 10-machine 39-bus test system shows the effectiveness of the algorithm.