Abstract: Objective Based on the Kalman filter function and stochastic models with ambiguity parameters,a newalgorithm is proposed for determining the parameters of the Kalman filter in RTK positioning.Theactual measured short baseline data of GPS/BDS is processed by a self-compiled GPS/BDS RTK posi-tioning program using this algorithm.It employs only a few epochs to give centimeter level positioningresults.Positioning results for three modes using BDS,GPS and BDS/GPS are compared and ana-lyzed.In case of short baselines,the RTK positioning accuracy of GPS/BDS is not improved noticea-bly relative to GPS or BDS.However it takes less time to get a fixed solution for GPS/BDS.This a-nalysis provide reference point for further GPS/BDS positioning research.