The invention discloses a fitting method for calculating the main coefficients of the boundary conditions of a groove wall based on experimental data, aiming at solving the present situation of lacking accurate calculation of the transonic wind tunnel slot wall boundary condition coefficients. In this method, the least square solution of the overdetermined equations is obtained by fitting the experimental data of the pressure coefficient near the wall and the deflection angle along the flow direction, which exclude the bad points, and the number of the main systems in the boundary condition ofthe wall is obtained by the least square method. The invention needs to eliminate the bad points of the original data, and then subtracts the reference data of the empty wind tunnel from the pressurecoefficient to eliminate the local fluctuation caused by slotting; based on the pressure coefficient-deflection angle nonlinear correlation,an overdetermined equation is established, the least squaresolution of the overdetermined equations is obtained by using the pseudo-inverse of the coefficient matrix, and the number of coefficients of the gradient term, the first order term and the second order term of the deflection angle in the boundary condition of the channel wall is obtained. The invention can improve the accuracy of the boundary conditions of the groove wall and guide the aerodynamic design and correction of the groove wall.