To improve the performance of a high-speed dot- matrix pulse jet generator in a printing machine and to optimize the printing effect of the machine, a mathematical model for the high-speed pulse jet generator was established and a sliding mode observer was designed. By building a feedback system based on the observer, the sensorless control of the high-speed pulse jet generator was realized to track the desired trajectory exactly, reduce the seating velocity of the valve core and to eliminate the vibration and noise greatly without increasing the cost of hardware. The experimental results show that the seating velocity has been reduced from 0.55 m/s for open loop control to 0.02 m/s for close loop one, the vibration and noise are almost eliminated, and the jet printing effect is improved obviously. The design result meets the industrial production demand when it is applied to a marking system for steel products and it provides theory foundation for design of the control units of high-speed pulse jet generators.