A mixing configuration defined as double two wave mixing is studied theorectically, which consists of two sets of two mutually beams interacting with the same photorefractive volume. Analytical solutions of the 2 order (2K 1 and 2K2) and the main combination components (K1+K2 and K1-K2) of the two primary space charge field are given. Under certain relations between K1 and K2, the 2 order and the main cross components are so large that can′t be neglected.