Abstract: The direct optimization method based on the mixed integer linear programming is proposed to solve the very involved nuclear power plant loading pattern search problem.By the introduction of 0-1 decision variables into the neutron diffusion equation,the original loading pattern search problem is converted to an equivalent mathematical programming problem,and then the loading pattern search and evaluation processes are completed synchronously by exploiting the powerful commercialized mathematical programming problem solver.In this paper,the feasibility of the proposed method is preliminarily demonstrated by its test applications to a 1D and a 2D problem.Numerical results reveal that the proposed method is capable of finding good loading patterns,even the global optima.However,since the current model still takes too much time to find the optima,the proposed method needs to be further improved before it can be ready for engineering application.