Abstract: When wind turbine generators（WTGs） adopt virtual inertia control to participate in grid frequency regulation, its essence is a kind of fast power response with time delay. However, the nonlinear effect of virtual inertia delay on frequency control is still unclear. Meanwhile, the virtual inertia has its inherent disadvantages such as high requirements for frequency measurement accuracy, long time delay, and amplified measurement errors by frequency differential link. Hence, the analytical solution for influential mechanism model of virtual inertia delay of WTGs and its substitutability research approach are proposed. Firstly, considering the delay of virtual inertia and droop control of the WTGs, which are approximately equivalent to the first-order inertia link, a system frequency response model for wind power frequency regulation using virtual inertia and droop control is established. Secondly, based on the Routh approximation method, the high-order model is analyzed by reducing the order, and the analytical expression of the system frequency nadir is obtained. Thirdly, the system frequency response model that only uses droop control for wind power frequency regulation is analytically solved, and the setting method for the droop control coefficient with the same frequency regulation effect as virtual inertia and droop control is given under the frequency nadir index. Further, under the setting of the droop control parameters, the relationship between the key indicators such as the maximum frequency change rate and steadystate frequency in the two control modes is compared. The purpose of replacing the virtual inertia with time delay can be achieved by changing the droop control coefficient appropriately, and the conclusion that the frequency regulation effect is better than that of virtual inertia and droop control can be obtained. Finally, a simulation model is established to verify the correctness of the analysis from the system frequency response dynamics, frequency regulation energy demand, and response power of WTGs etc.