In order to address the issues of the non-detection zone and extended detection time in existing islanding detection methods, an improved reactive power disturbance islanding detection method incorporating the effects of constant small perturbation and compound frequency difference is proposed. The relationship between the reactive power perturbation injected by distributed generation and the frequency offset at the point of common coupling is analyzed. A reactive disturbance generation method that combines constant disturbance and positive feedback of the square of frequency deviation is designed. In this method, a constant perturbation generates an initial frequency offset, while additional perturbations enhance the frequency difference-reactive power perturbation response speed and reduce the impact of frequency fluctuations in grid-connected mode. Parameters such as disturbance coefficient and disturbance period are designed by synthesizing the requirements of islanding detection time and the impact of disturbances on power quality, and the implementation process of islanding detection is provided. Simulation results indicate that the improved reactive power disturbance islanding detection method effectively overcomes the challenges posed by the non-detection zone. Compared with the traditional positive feedback reactive power perturbation method, the islanding detection time is significantly reduced, with a maximum reduction of 52.5%, while almost does not exacerbate the impact on power quality. These results substantiate the correctness and effectiveness of the proposed method.