A waste soil improving method of soil pressure balance shield of a high water pressure and high permeability sandy stratum comprises the steps that A, 0.8-1.2 parts by weight of sodium bentonite, 0.04-0.06 part by weight of carboxymethyl cellulose and 10 parts by weight of water are mixed, stirred continuously for 10-15 min and then placed in a container to stand for 20-24 h, and improved slurry is obtained; and B, before driving, the water containing state of rock soil of an excavation face is measured, in the soil pressure balance shield driving process, the improved slurry is injected into a soil bin of a shield machine, if the measured water containing state of the rock soil is a supersaturated state, the ratio of the injection volume of the improved slurry to the waste soil entering volume of the soil bin is 1:2-3.4, and otherwise, the ratio of the injection volume of the improved slurry to the waste soil entering volume is 1:3.5-4.5. By improving waste soil through the waste soil improving method, gushing can be better avoided and relieved during soil pressure balance shield construction, and the influence on the engineering progress is less; and the cost of subway construction is reduced.