This paper studied the multipath error and noise of space-borne GPS code measurements collected from American BlackJack receiver onboard CHAMP, GRACE-A and Jason-2 satellites and the Chinese-built receiver onboard HY2A, ZY3 and TH1 satellites. The emphasis was paid on the variation characteristics of the multipath error and code noise and their impact on real-time onboard orbit determination. The result demonstrated that the C/A and P1 codes observation precision of the Chinese-built receiver was worse than that of American BlackJack receiver, and the P2 code precision of the Chinese-built receiver was superior than that of American BlackJack receiver. The code multipath errors of HY2A, ZY3 and TH1 satellites increased along with the decrease of elevation angles of GPS satellites, and the maximum errors are up to 3.6 m, 1.8 m and 0.7 m, respectively. The orbit determination experiments showed that the monotone increasing multipath error can lead to the systematic bias on the position of real-time onboard orbit results in the radial and tangential directions.