To deal with the main problems which affect the metering precision in metering device for pulverized materials such as “arching of materials”and “non-uniform discharge”etc，the mechanical structure of the metering device were studied. The hopper structure,arching-detractive device and the transport spiral were improved to resolve the problems in fluency and uniformity of materials transportation and to elevate the metering precision. Combining with the materials characteristics,the effect of the mechanical structure on the system precision is analyzed according to the stability of the air pressure in the hopper and the change of the materials pressure etc. The results show that when combining with automatic control system the dynamic metering precision of system is higher than ±1%，the requirements of on-line metering of propellant and explosive production process are satisfied.