The work aims to solve the edge effect problem during the ion beam figuring on the surface of the optical elements. The method of extending the dwell time mesh on the basis of the surface shape sampling mesh was used to suppress the generation of edge effects, i. e. the mesh range of the dwell point was extended, so that the number of dwell points that removed the sample points at the edge portion of the component was the same as in the middle portion and the extension distance was greater than the ion beam radius. The truncated singular value method was used to solve the dwell time of the linear equations model, and the causes of the edge effects in the simulation results were analyzed. When the dwell time adopted the same meshing as the surface error, the residual surface did not converge and a serious edge effect occurred. When the truncation parameter k=80, its PV value decreased from the initial 104.489 nm to 11.675 nm, and the RMS value converged from 28.009 nm to 1.572 nm with no edge effect. With the above-mentioned simulation results as experimental setting parameters, ion beam figuring experiments were carried out on planar optical elements. Before and after figuring, the PV value decreased from 102 nm to 37 nm and RMS decreased from 23 nm to 2 nm. The experimental results basically verify the validity of the simulation results. The method of dwell time mesh extension can avoid the edge effect. On this basis, in the ion beam figuring, the PV value of the surface shape and the roughness of the optical components can achieve a very good convergence effect.