Variable fertilization technology is an important part of precision agriculture. According to the requirements of agricultural production, the SYJ-2 type three-point suspension liquid variable fertilizer machine was designed which was matched with wheeled tractor. Taking the single chip microcomputer as the core processor and the electromagnetic proportional adjusting valve as the execution unit, the control system for liquid variable fertilizer and the upper computer software works in concert with hardware were designed and programmed for collecting data and sending the command. The key components, which called rotary pricking hole mechanism, used five congruent oval gears to drive. The liquid fertilizer flew in the cavity of rotary pricking hole mechanism. This agency reduced the external connecting hoses at the same time and prevented the pipe twine. The function of the liquid fertilizer distributor was opened and closed timely. The mechanism could achieve discontinuous injection of liquid fertilizer, then complete the injection operation of liquid fertilizer. The structures for distributor and intracavity rotary pricking hole mechanism were designed at the same time. The field experiment results showed that the fertilization depth was 12~15cm below the soil surface, and the fertilization accuracy was 99.1%, which meets requirements of liquid fertilizer for variable fertilization.