Virtual synchronous generators can provide the virtual inertia for power grids via simulating the characteristics of traditional synchronous generators. Nowadays, it is widely used in distributed generations. However, under unbalanced grid conditions, problems such as power oscillation and current distortion will occur. By introducing a new power reference calculation method which derived from the 1/4 cycle delay of the grid voltage, a power oscillation suppression strategy for virtual synchronous generators under unbalanced grid conditions is proposed in this paper. Compared with the conventional strategies which based on the calculation of the positive and negative sequence current reference, the power oscillation is suppressed and the current distortion is improved, at the same time, the proposed strategy is simpler because of not requiring the positive and negative sequence extraction. Simulation results show that the proposed strategy is correct and effective.