Abstract: For quantitative and scheduled trace liquid injection problem，the author designed a set of quantitative and scheduled liquid injection system based on single chip microcomputer， designed and developed the injection system hardware and single chip microcomputer control software，respectively. The system drove and segmented pulse signal of stepper motor with single chip microcomputer，to produce a tiny amount of angular displacement and realize high precision injection；at the same time，the harmonic reducer can control the angular displacement accurately and realize the linear feed；the precise control of the plunger was achieved with screw micrometer rod to complete the trace injection. Generally speaking，the trace injection was completed and the injection effect was improved.

Key words: single chip microcomputer, stepper motor, angular displacement, harmonic reducer