The virtual oscillator control (VOC) strategy is a new distributed control method with great application potential in off-grid and grid-connected inverters. However, when load variations and nonlinear unbalanced loads are connected to the system, the off-grid inverter system based on VOC will exhibit problems such as frequency deviation and harmonics. Considering the above-mentioned deficiencies, by analyzing the impact of mixed load on the power system, this paper proposes an improved VOC strategy. The technology of positive and negative sequence separation of voltage and current is introduced and a secondary frequency compensator is designed. Also, the voltage-current double closed-loop structure is improved to further augment the system's ability to suppress harmonics. A simulation model of the inverter off-grid system is built on the Matlab/Simulink platform. Compared with conventional VOC, the effectiveness of the proposed control strategy in solving the problem of frequency deviation and harmonic suppression is verified.