There is great interest in using the strained Si CMOS technology lately for carrier mobility enhancement. Intrinsic carrier concentration is the important physical parameter for the characterization of strained Si materials and the determination of the electrical properties of strained Si-based devices. Starting from analyzing the band structure of strained Si/（001）Si1-xGex，the model of its intrinsic carrier concentration related to Ge fraction （x） at 300 K was established with the frame of K.P theory，which provides valuable reference to the understanding on the strained Si-based device physics and its design.