Global Navigation Satellite System(GNSS) -based passive radar is a hotspot of current research. In the positioning method based on the sum of distance, the time synchronization error and positioning error of GNSS will reduce the positioning accuracy. Considering the above errors and combining the signal characteristics and parameter measurement capabilities of the four major GNSSs in the world, the three-dimensional localization accuracy expressions and the Cramer-Rao Lower Bound(CRLB) for the system of multi-transmit multi-receive are derived. Through simulation analysis, the relationship between the number of satellites or receiving stations and the localization accuracy is revealed. When the satellite position errors are ignored, the percentage increases in localization accuracy caused by the number increases of receiving stations are the fixed values for any number of radiation sources; if the satellite position errors increase, the improvement in positioning accuracy by increasing the number of receiving stations will decrease. The obtained conclusions can provide a theoretical reference for the selection of GNSS-based passive radar radiation sources and the deployment of receiving stations.