Abstract: To solve the unequal transfer problem when the number of tasks differs from the number of vehicles,a model for two-dimensional unbalanced assignment problems was established,and the particle swarm optimization(PSO) was adopted to obtain its solution.Numerical simulation was conducted under different unequal assignments,and the simulation result was compared with the result based on the completed enumeration.The research result shows that PSO is superior to the completed enumeration in the probability of getting the optimal solution and the convergence speed,so the established model and PSO can be used for getting a satisfactory transfer plan.