Abstract: This paper proposes a method aimed at reducing frequency fluctuations in an islanding AC microgrid including variable frequency load under disturbance. The method involves coordinated frequency regulation of variable frequency load based on the coupling characteristics of DC voltage, motor speed, and frequency. In the past, the inertia of capacitors and motors of variable frequency loads was hard to be coordinated to participate in frequency regulation, which could cause voltage or speed violations and lead to inverter lock-up or motor instability. To address this challenge, this paper proposes a coordinated frequency regulation approach that utilizes virtual synchronous machine and vector control, with the voltage-speed coordinated frequency modulation term. This term incorporates a frequency differential signal on the inverter side, allowing for rapid response when disturbance occurs. A small signal model is constructed, and the coefficient is adaptively adjusted based on the voltage and speed to dynamically optimize the inertia releasing ratio. The adaptive coefficient tuning method is presented based on the frequency dynamic response in time domain. An optimal interval tuning method of weight coefficient is proposed according to the sensitivity analysis. The islanding AC microgrid model is built on the RT-LAB platform, and the results show that the proposed strategy can improve the frequency quality under disturbances through the coordination response of the capacitor and motor inertia.