The transferred electron effect between different valleys in AlGaAs/GaAs/AlGaAs heterost-ructure is studied using the one band two valleys model in this paper. Taking the contributions from various electric field and the band offset and current are derived. The tunnelling probabilities and currents for various hetorostructures, alloy components and electric fields have been calculated. The dependence of transferred electron effect on the heterojunction interface, the band structures of the well and barrier materials, and the electric field is discussed. The computed tunnelling current agrees with the experimental results, and so the effectiveness of this model in the research of many valleys system is demonstrated. Furthermore, the difference between this transferred electron effect and the well known Gunn effect is pointed out and its application in the developing 9f semiconductor devices is discussed.