The principle and process of producing molybdenum powder via reduction reaction of molybdenum trioxide at lower temperature in a N2-H2 system were researched. The effects of hydrogen concentration, temperature, and volatilization rate of molybdenum trioxide on particle size were analyzed. The experimental results showed that the optimal process parameters were 770°C-790°C in 60min when the hydrogen flow rate was 700mL/min. Particle size of superfine molybdenum powder was less than 4μm. The concentrations of hydrogen, temperature and volatilization rate of molybdenum trioxide have great effect on the particle size of superfine molybdenum powder.