Two parameters, pixel expansion and contrast, are very important in visual cryptography. It 's very difficult to optimize both of them in theory. Based on combination, A (2, n) scheme, which existence has been proved theoretically, has been proposed in this paper. Meantime, the method of construct has been carried out. Simulation results demonstrate that this scheme can balance performance between pixel expansion and contrast, i.e., the contrast is close to optimality, meanwhile the pixel expansion is the minimal.