The ZN-3 sounding rocket is an important instrument used for the sounding of space science. Because of its few using quantity and the expensive scientific instrument it carries, not only high reliability is required, but also the advanced performance and econo mization are demanded. How to accurately deal with the relationship among these factors in technical design is very important. In this paper，through analyses and discussions of correctly dealing with the technical problems，snchas the determinants of stage number，formulatiog optimum program of thrust，reliability of construct and evaluation of fests etc. The methods unifying the general reliability，advancity and econom zation of the rocket are reached.