The invention provides a preparation method for a SiGe HBT. N type impurities are implanted in ions into a second polysilicon layer, and then annealing with laser in a proper wavelength, instead of normal rapid thermal annealing, is used to activate the N type impurities; and thus, energy of the laser in the proper wavelength only has effect within the thickness range of the second polysilicon layer, and does not influence a SiGe base region under the second polysilicon layer. Therefore, on the premise that the N type impurities which are implanted in ions into the second polysilicon layer are effectively activated, boron in the SiGe base region is avoided form further spreading, further barrier effect of heterojunction is prevented, and the SiGe HBT has better performance.