| In view of the present synchronous grouting diffusion model of shield tail, whose premise was that the longitudinal and circular flow of slurry was independent of each other,without considering the correlation of slurry flow,the mechanism of synchronous grouting diffusion mode in shield tunnel was analyzed, and the theoretical model of synchronous grouting longitudinal-circular integral diffusion of shield tail was established, which was based on Bingham fluid constitutive model and fluid mechanics principle. Through space and time domains discrete approach, a numerical algorithm to solve the theoretical model was designed. Combined with engineering examples, the theoretical model and numerical algorithm were validated. The results were compared and analyzed with the existing circumferential independent diffusion model. The results show that: compared with the circumferential diffusion model, the longitudinal-circular integral diffusion model improves the assumed conditions, and is more close to the actual situation of the project, which does not need to introduce sensitive assumption parameters such as the thickness of the ring cake. As a whole, the slurry pressure trends to be dominated by gravity, small in the upper part and large in the lower part. And the vertical gradient is about 16 kPa·m-1. But the slurry pressure distribution in the local area near the grouting hole is relatively complex, which is related to many factors such as the grouting hole location, the direction of slurry flow and the pressure difference between the grouting pressure and the environmental pressure.