Abstract: To solve the problems of high equipment cost，expensive operational cost，large monitoring region and less observation points for the PM2. 5 monitors both at home and abroad，a low-cost and high-precision PM2. 5 assistant monitoring method was proposed based on the national monitoring network． The system converts from particle number concentration to mass concentration by using DSM501A as acquiring PM2. 5 concentration sensor． Through deploying concentration sensors in monitor region，a PM2. 5 mass concentration network map was constructed by GPＲS network and construction of parametric surface． The study fills the blindness between existing national monitoring points． The forecast algorithm is established by Gaussian elimination algorithm and historical data． The experimental result showed that the measured data agreed basically with those of the national monitoring points． The system would be applied widely in the future．