Abstract: Perilous rock is one of main geologic disasters in mountain area of China.Safe net system is a passive control technique for rockfall in recent years.To study safe net system,on the one hand,much attention is paid to system itself without care of characters of rockfall trace and initial motional parameters.On the other hand,study of rockfall doesn’t comply with the characters of safe net system.So,the authors simplified the motion of rockfall as equivalent frictional motion,and the imperilled area by rockfall was estimated.Additionally,by classifying the motion of rockfall on slope surface into intersected bouncing,rolling and sliding,the whole trace of rockfall was calculated.Finally based on the results of rockfall trace calculation combined with the characters of safe net system,the authors presented the conception and method of design of safe net system.Engineering application as wellas comparison with typical rigid passive control techniques showed that the safe net system had advantages of better applicability to engineering surroundings,less influence on environment,cheaper and shorter time limit for projects.