Abstract: Velocity is a crucial parameter for describing and characterising the motion state of a carrier. Consequently, numerous applications and research projects have set high standards for the accuracy of velocity determination. GNSS velocity determination technology has become an important means of speed measurement by virtue of its high accuracy and efficiency, and has been widely used. In the related research of GNSS velocity determination, there are more researches on velocity determination algorithm and accuracy evaluation, but the research on velocity determination stochastic model is almost blank, and the application still mostly uses the stochastic model and parameters of positioning. In this paper, based on the single-point time-differenced carrier phase (TDCP) velocity determination algorithm and the least squares estimation, we study the construction method of elevation-dependent stochastic model of the GNSS velocity determination, and establish the dual-frequency carrier phase velocity determination elevation-dependent stochastic model of the GPS/BDS/Galileo triple-system, which takes into account of the type of receivers and the orbit of the navigation satellites. Tests of the TDCP velocity determination elevation-dependent stochastic model show that the receiver type and navigation satellite orbit are important factors affecting the stochastic model, and the constructed stochastic model for velocity determination improves the accuracy of joint multi-system velocity determination. Using the newly constructed elevation-dependent stochastic model, the accuracy of dual-system and triple-system velocity determination of GPS, BDS and Galileo can be improved by up to 5.67%, 5.81%, 5.21% and 9.58%, respectively.