In order to solve the problem of reusing a large amount of rock slag when the slurry shield passes through the weathered rock stratum, relying on the Nanjing Heyan road crossing-river project, the rock slag is used to replace part of commercial sand to prepare the synchronous grouting slurry. The fluidity, consistency, setting time, bleeding rate and strength of the slurry are tested through laboratory tests, and the performance and micro morphology of shield synchronous grouting slurry made of weathered rock slag are analyzed. The results show that: with the increase of the proportion of rock slag replacing commercial sand (denote as the replacing ratio), the fluidity, consistency and bleeding rate of the slurry decrease, while the setting time shows a decreasing trend, and the compressive strength gradually increases after 1 day. When the replacing ratio is 50% to 85%, all properties of the slurry can meet the requirements of engineering construction; when the replacing ratio of rock slag is 85%, the fluidity and consistency of the slurry are close to those of the on-site slurry, the setting time is shortened from 10.6.h to 7.3.h, and the 1-day compressive strength is nearly doubled. Kaolinite phase minerals contained in the rock slag will electrolyze Al3+ in water, which promotes the formation of C-S-H gel in the slurry, and is the fundamental reason for shortening the setting time of the slurry and increasing the compressive strength of the slurry.