When single satellite navigation system be used for single point positioning,existing following problem: numbers of visible satellite are low and accuracy of positioning is low.This paper studies the modelcombination of BDS/GPS/GLONASS systemof single point positioning,and a scheme of combined weighting is put forward.The characteristic of combined weight-method is that inside of system adopts elevation to determine weight-value,the inter-system adopts Helmert-Variance to determine weight-value.The experimental results show that the number of visible satellite of combination of BDS/GPS/GLONASS system are than any single-system,and the number of satellites are greatly increasing,and significantly improve user-satellitegeometry,and greatly improve accuracy of positioning.Positioning performance of combined weighting is superior to the traditional weighting.