By solving Poisson equation, models of voltage and electric field distribution are build respectively in collector junction depletion layer of SiGe HBT (heterojunction bipolar transistor) with intrinsic SiGe layer. On this basis, models of the collector junction depletion layer width and delay time are obtained. Applying MATLAB, the impact of physical and electrical parameters on SiGe HBT collector junction depletion layer width and depletion delay time are quantitatively analyzed. When base doping concentration and collector junction reverse bias are large, the depletion delay time is quite long. But, when base doping external diffusion depth and collector region doping are large, the depletion delay time is quite short.