Abstract: With the continuous development of GNSS, the research on high-precision time transfer based on precise point positioning (PPP) technology has become one of the key technologies in the field of time and frequency. In this paper, the receiver clock offset of the BeiDou-3 system is taken as the research object, and the influence of ionospheric-free and uncombined PPP models on time transfer is analyzed. Firstly, the differences between the two PPP mathematical models are derived, and the observation data of two external hydrogen atomic clocking stations of DOY 79～81 in 2024 are selected for analysis. The results show that the receiver clock difference calculated by the two PPP models fluctuates within 0.15 ns, and the corrected Allan variance value is similar. For the BRUX-USN7 time link analysis, the time transfer results fluctuate within 0.8 ns within three days, the Allan variance values of the two models for solving the clock offset correction are approximate. In summary, although the two PPP models have different theoretical models for the numerical solution of the clock offset, there is no significant difference between the two models in terms of the clock offset solution and time transfer, the uncombined model can be used for time transfer and has more advantages in retaining ionospheric information.