The third boundary value problem for a multidimensional convection-diffusion equation with memory effect and non-local (integral) source is investigated. To solve numerically the multidimensional problem, a locally one-dimensional difference scheme is constructed, the essence of the idea of which is to reduce the transition from layer to layer to sequential solving of a number of onedimensional problems in each of the coordinate directions. Using the method of energy inequalities for the solution of a locally one-dimensional difference scheme, an a priori estimate is obtained. The main research method is the method of energy inequalities. An a priori estimate of the LOS solution is obtained, from which follow uniqueness, stability, and convergence of the solution of the difference problem to the solution of the original differential problem at a rate equal to the approximation error. Numerical experiments were carried out.