The invention discloses an SPH (Smoothed Particle Hydrodynamics) algorithm based symmetric boundary treatment method. The method is characterized by comprising the following steps: creating a simulation model to be subjected to simulation analyzing, and initializing; calculating the pressure value, stress tensor and artificial viscosity value of each particle corresponding to the simulation model; performing search analysis on the simulation model within each set time step; calculating a state equation and control equation corresponding to the simulation model; if a symmetric boundary is in the simulation model, performing acting pair information supplementation on the simulation model; and outputting a corresponding simulation result based on the set end condition. According to the method, the existing action pair information is screened and supplemented, so that the additional time of generating mirror particles and researching can be saved while the operation of additionally generating the mirror particles and dividing background grids for the mirror particles to research is avoided, and thus the symmetric boundary treatment and the common researching calculation are unified to treat.