Abstract: Based on the arithmetic of longevity prediction for WSN（Wireless Sensor Networks），the arithmetic for MWSN has been further studied，and the mapped chart has been put forward from structure angle，and the mapping function which only related to best neighbor number has been given，thereby getting the arithmetic of longevity prediction by random distributing.Moreover，the longevity has been shorted because of the frequent update of dynamic networks，so from energy-saving angle，the influence has been optimized by genetic algorithm，and the universal energy-saving algorithm which solve the problems of MWSN has been proposed.Simulation experiment attests to above questions’ validity.