This paper introduces in detail the working principle of Si/SiGe Quantum cascade laser(QCL). Appropriate parameters are used to calculate the hole subband structure of Si/Si1-xGex quantum well using a six-band k·p method.The dispersion relation and energy band for different layer thickness and compositions are investigated. Meanwhile,the energy separations between hole subbands in Si/Si1-xGex/Si quantum wells are also analyzed. Finally the calculated results are used for the Si/SiGe QCL design，which will be beneficial to the structure optimization of Si/SiGe QCL.