In order to solve the problem of unpredictable penetration rate in soil-rock mixed ground for shield TBM. In this pape, combined with the rock breakage process and the cutterhead force characteristics, the rock breakage mechanism of the mixed ground and the impact of the mixed ground on shield TBM tunnelling performance was analyzed. Then, based on Shenzhen Metro Line 12, information on operating parameters, geological parameters, and muck parameters was collected, the tunnel face information of the soil-rock mixed ground were obtained, and then a database containing 9 interval sections of soil-rock mixed ground was established. Finally, by multiple non-linear regression analyses, the penetration rate prediction model of the soil-rock mixed ground with the ratio of soil in the tunnel face and the penetration rate of rock ground as the main influencing parameters was proposed. The correlation coefficient between the predicted values and measure values of the penetration rate of this new model was 0.85, and the model prediction results were reliable. The parametric analysis of the model show that the change of the penetration rate is extremely sensitive while the ratio of soil in the tunnel face exceeds the critical value of 0.8. On the contrary, the penetration rate slowly decreases and tends to the average penetration rate of the rock ground. The research results can provide a reference for the optimized construction parameters and developed construction planning of shield TBM tunnelling in the soil-rock mixed ground.