Abstract: The increasing penetration of distributed energy sources makes the imbalance of the active distribution system much higher than that of the traditional distribution network. This paper investigates an optimization model for distributed generation（DG） output of the unbalanced distribution system with the minimization of network loss and the maximization of DG output as the objective functions. First, an analytical expression for the sensitivity of network loss to DG output with voltage as the decision variable is derived based on the unbalanced linear tidal model of the immovable point theorem, which is introduced into the general single-objective optimization mathematical model of DG output in the unbalanced distribution systems. Then, a multi-objective optimization model considering the maximization of DG output is proposed and the modulation of the scaling factor is given.Finally, the effectiveness of the proposed method is verified by the simulation of arithmetic cases.