A prepn. method of silicon thin film heterojunction solar cell includes following steps: cleaning substrate, semiconductor cleaning technology is used to do primary cleaing to substrate surface, then do ultrasonic cleaning in deionized water several times; nitrogen blow drying; prepare nitrinsic amorphous silicon layer by heater chemical vapour phase depositing technology, tungsten filament temp. is measured by pyrometer, temp of heater and sample are determined separately by two electric thermo-couples, temp. is controlled by electric temp. controller; to react and grow thin film on substrate surface; to redeposit a transmitting layer on intrinsic amorphous silicon thin film; front and back electrodes forming, sputtering technology is used to form front and back electrodes; finally to proceed vacuum heat annealing process. The thin film produced by the invention has illumination stability, the photoconduction gain can reach to 10 to the power 6 on Am1.5 100mW/cm2 standard illumination.