The invention provides a filling stability grouting method for mobility sand bed foundation soil under dynamic pressure water and the method is used for grout strengthening of sand bed foundation soil under a traffic tunnel. The filling stability grouting method comprises the following steps that (1) a tunnel structure part with uneven settlement is subjected to hole arrangement, and an orifice casing pipe is installed in a hole; and (2) drilling is conducted, a concrete floor is drilled through, and the sand bed foundation soil under the concrete floor is drilled by 1-3 cm, so that a first pouring conducting section is formed, and after the first pouring conducting section is subjected to hole forming, cement paste is poured into the first pouring conducting section; drilling is conducted under the first pouring conducting section, and the drilling depth is 1-3 m, so that a second pouring conducting section is formed, after the second pouring conducting section is subjected to hole forming, cement paste is poured into the second pouring conducting section, and in this way, sectioned drilling and grouting are conducted from top to bottom in sequence; and when each pouring conducting section cannot be subjected to hole forming in the drilling process, an early solidification stable material is poured into the drilling position. According to the filling stability grouting method provided by the invention, the technical problems that hole forming of a mobility sand bed under the pressure dynamic running water is difficult, the cement paste is difficult to pour, and filling stability is difficult to achieve are solved.