The invention provides infrared absorption doped silicon and a preparation method thereof. The preparation method involved in the invention is characterized by including the following steps of: step 1, adopting a TRIM program to simulate the ion distribution of different types of ion-implanted silicon wafers, wherein the simulated ion species are selected from B+, P+, As+, Si+, or/and Ar+, He+, H+, Kr+, Xe+; during the simulation, the energy is set to 10-1000keV, and the simulation dose is 1014-1018ions/cm2; the target of simulation is that: after the silicon wafers are implanted, the ion distribution can enter the silicon body from the silicon surface, the depth distribution ranges from 2nm to 1000nm, and the transmittance of the silicon wafers after doping ions is 0; and step 2, performing ultrasonic cleaning on monocrystalline silicon wafers, and then drying with an air gun; step 3, performing ion implantation on the monocrystalline silicon wafers based on a simulation result; and step 4, performing thermal annealing to obtain the infrared absorption doped silicon.