This disclosure provides a high-voltage terahertz strained SiGe/InGaP heterojunction bipolar transistor and a preparation method thereof. An InGaP material has characteristics of a high carrier mobility of the InP material and a forbidden band width of the GaP material, so that the present disclosure employs the N-type In1-xGaxP layer as the collector to improve the frequency and power characteristics of the device, and realize the system integration of terahertz band chips. Further, the present disclosure utilizes the characteristics of the above materials and takes an advantages of “energy band engineering”, uses the In1-xGaxP (x=0-1) is used as the material of the collector of the SiGe-HBT, the composition molar ratio X of In and Ga is appropriately selected, such that the materials SiGe of the collector and the sub-collector have the same lattice constant, so as to effectively improve interface characteristics of InGaP and SiGe materials.