The invention discloses a layer model establishing method for observation system parameter argumentation. The method comprises the following steps: a layer to be processed is subjected to meshing operation according to layer information available in a work area and earthquake root mean square velocity; depth values and inclination angle of all layer grids are calculated via interpolation, earthquake root mean square velocities of all discrete spots are converted from time-speed pairs to depth-speed pairs, and reflection time and root mean square velocity values are obtained according to layer depths of the discrete spots; after all layer grids are checked, reflection time and assigned root mean square velocity values of layer grids without reflection time and assigned root mean square velocity values can be obtained via grid index-based gradual extrapolation equidistance inverse ratio weighting interpolation; finally a layer model containing depth, inclination angle, reflection time and root mean square velocity information is built. Via the method, reliable basic data is provided for design of an earthquake observation system in a mature oil gas exploration region, and the method can be applied to industrial production of seismic prospecting.