The position to catalyze a cloud can be determined by observing its physical quantities such as radar echo intensity,distribution of water content and temperature.In the triangle consisted of a radar station,a launching-site and an object cloud,the launching azimuth can be worked out.According the height of the seeding position observed by radar and the ballistic parameters of rockets or anti-aircraft guns,the launching elevation can be determined too.Thus,eye observation blindness can be properly reduced in weather modification actions.