The cavitation phenomenon in the process of underwater motion of submarine launched ballistic missile changes the mechanical environment of missile body and seriously affects the flight attitude of missile. In order to accurately analyze the change rule of the missile’s flight attitude under the cavitation condition, the qualitative analysis and quantitative calculation are used to analyze the influence mechanism of the cavitation phenomenon on the missile’s motion attitude, and the force condition of the missile body under the cavitation condition is modified. The change of the missile’s pitch attitude under the cavitation condition is compared and calculated in the Matlab simulation environment. The conclusion is close to the experimental data, which can provide reference and theoretical basis for the further study of underwater trajectory of SLBM.