RNAV positioning mathematical model of DME/VOR is established and the error factors of RNAV is analyzed. Referencing the MLS angle error filtering theory in ICAO, the digital filter is designed based on the bilinear transformation method. The RNAV accuracy prediction algorithm is put forward. The experiment results show that the RNAV accuracy prediction algorithm based on DME/VOR navigation source is correct and it can serve as a reference to the further selection of land-based navigation station.