A kind of single-ended fly-back switching power supply, which mostly be used as the power supply of one-chip computer system based on TOP224Y, is researched in this paper. The power supply outputs two channels DC voltages of + 5V and + 15V. its method of engineering design is brought forward according to the quality of TOP224Y , and its peripheral circuits are analyzed and dis cussed in terms of characteristics of the one-chip computer power supply. At last, the performance of the power supply is verified through experiments.