The invention discloses a real-time monitoring and grouting reinforcement method for weak surrounding rock tunnel building and belongs to the technical field of tunnel engineering. The method comprises the following steps that tunneling is stopped after one cycle tunneling task is finished for a tunnel; a tunnel face is closed through net spraying, a hole is drilled along the tunnel face, and an advanced small pipe is driven in; grouting reinforcement is carried out on the tunnel face through the advanced small pipe; the grouting amount is controlled through grouting pressure, and grouting is finished after the final grouting pressure reaches 2-3 MPa; after grouting is finished, a rock core is drilled in the grouting body, and the grouting condition is examined; the grout filling condition is observed, and the rock core is inspected; if the rock core strength and the grout filling condition reach construction standards, next operation cycle is carried out. According to the method, the safety of weak surrounding rock tunnel building can be improved, unnecessary personnel losses are reduced, measures are reasonable, and safety and controllability are achieved.