Since the single-phase grid-connected inverter system lacks a degree of freedom, it is impossible to directly convert the amount of AC in the static synchronous coordinate system to the amount of DC based on the dq coordinate system. The virtual orthogonal variable obtained by directly transforming the actual physical quantity by 1/4 power frequency cycle and the introduction of complex algorithm, seriously affects the dynamic response characteristics of the system and increases the system complexity. In this paper, a method based on indirect delay to construct orthogonal virtual quantity is proposed. Firstly, the real physical quantity is delayed by a small time, and then the obtained delay quantity and real physical quantity are used as input quantity. The required orthogonal virtual quantity. The method uses a small delay to replace 1/4 of the power frequency cycle delay, and does not need to introduce complex mathematical algorithms, which greatly improves the dynamic response characteristics of the system. Finally, the effectiveness and correctness of the proposed method are verified by MATLAB simulation.