The invention discloses a coral sand stratum barrel-shaped foundation reinforcing device based on MICP and a mounting method. The device comprises a barrel-shaped foundation, a water pumping hole, a grouting master pipe, a grouting steel pipe, a one-way valve, a backflow pipe and the like. A draining hole connected with the grouting steel pipe is formed in a barrel-shaped foundation top plate, thegrouting steel pipe is arranged to be like a Chinese character mi, and grouting holes are formed in the grouting steel pipe along the outer side wall of the foundation at equal intervals. The backflow pipe is arranged on the exterior of the foundation and used for recovering and circulating of slurry. According to the coral sand stratum barrel-shaped foundation reinforcing device based on the MICP and the mounting method, through a microbial rock forming effect, a coral sand stratum is reinforced, the cementation effect between gravel as well as between the gravel and a structure object can be effectively improved, and the bearing capacity and the stability of the foundation are improved; and the MICP technology has no bag influence on the environment and ecology and is an environment-friendly technology suitable for coral sand stratum reinforcement.