In this paper, the duplex yield character (DYC) of dualphase steel has been discussed. The results of the tests show that the DYC is due to the martensite deformation from the elastic state to the plastic state and the microvoid formed from the interphase boundaries. The DYC is directly affected by the phase ratio and the shape of structure. According to the different deformation character of the duplex phase, the uniform deformation of dual phase steel divide into three stages.