This paper proposes a hybrid islanding detection method for inverter-based distributed generation units. Firstly, this paper carries out a comprehensive characteristic analysis and obtains design principles for the hybrid method in inverter-based DGs. Then, based on these principles, the proposed method combines the passive method of voltage unbalance and total harmonic distortion(VU/THD) detection and the active method of bilateral reactive power variation(BRPV). In specific, the BRPV method is only triggered when the islanding condition is suspected by VU/THD method. Doing so, the islanding detection performance can be improved significantly without reducing the power quality. In addition, this paper modifies the conventional VU/THD method to realize fast and accurate detection, and the threshold setting principle is analyzed for the first time based on equivalent circuit approach. Comparison analysis reveals that the proposed method has a more satisfactory islanding detection performance for inverter-based distributed generation units. Simulation and experimental results under various conditions based on IEEE Std. 929 and IEEE Std. 1547 were carried out to verify the islanding detection performance of the proposed method.