This paper presents a diode-based two-branch predistortion circuit. The predistortion circuit contains two nonlinear branches, including the main branch and the auxiliary branch. The main branch is a diode based nonlinear generator. The auxiliary branch consists of variable attenuator and nonlinear generator. By adjusting the voltage bias of nonlinear generator and variable attenuator, different combinations of amplitude and phase characteristics can be obtained. Compared with single nonlinear generator, this two-branch predistortion circuit increases the slope of amplitude characteristic.