To analyze the effect of Oven Controlled Crystal Oscillator (OCXO) short-stability on the accuracy of Precise Point Positioning (PPP) of navigation enhancement system. Firstly, this paper introduces the concept of OCXO short-term frequency stability, and then inverts the noise according to its short-term stability characteristics. Then, the PPP positioning model of the system based on OCXO short-term stability noise inversion is established, and OCXO inversion noise with different short-term stability magnitude is introduced into the model, and the final PPP positioning accuracy of the system is analyzed and compared. The experimental results show that the OCXO with the short-stability order of E-13 can meet the centimeter-level positioning requirements of the system in the medium and long observation periods (<1 000 s) without the control section to adjust the on-board time-frequency. The analysis can provide some reference for the time-frequency index design of LEO navigation enhancement system.