This paper discusses the inverse problem of determining a spacewise unknonwn source for the two dimensional modified Helmholtz equation in a half strip domain.This problem is ill-posed,i.e.,the solution does not depend continuously on the data.A regularization solution of the inverse problem is obtained by the quasi-reversibility regularization method.For the regularization solution,convergence estimate is obtained between the regularization solution and the exact solution.The numerical example shows that t...