The doubly-fed wind power system lacks the ability of independent support of voltage and frequency when it is in off-grid operation, and there are problems such as slow response speed and high voltage harmonic content. In order to solve these problems, an off-grid control strategy of grid-forming doubly-fed wind power system based on model prediction is proposed. Firstly, the virtual synchronous generator (VSG) control is adopted in rotor side converter (RSC) to make off-grid doubly-fed wind power system reflect the voltage source characteristic. Meanwhile, according to the similarity of the dynamic characteristics between the DC capacitor and the synchronous machine, the inertial synchronous control is adopted in the stator side converter (SSC) to realize the operation of the whole off-grid system without phase-locked loop, which improves the immunity. Secondly, the current prediction model of RSC and SSC is established, and model predictive control (MPC) of both sides of the converter is realized, which accelerates the response speed and reduces the harmonic content of stator voltage. Finally, the effectiveness and practicability of the proposed off-grid control are verified by simulation analysis.