Aiming at solving the real-time computation of the satellite orbit in GNSS (Global Navigation Satellite System) emulator with multiple constellations, the Newton and Hermite polynomial interpolation algorithms were analyzed and compared by computing efficiency and accuracy. The precision of the satellite position and velocity (PV) performed better by adding “window” in the Newton algorithm. The computation examples show that the real-time and high-precision computation of the satellite PV is achieved with position at the equation interval epoch known and velocity unknown. The results also show that the new method speeds up the computation seven times faster than the direct ephemeris calculation, and yeilds better performance in orbit precision than the 3-order Hermite Interpolation, for the position error is less than millimeter and the velocity error 1e-5 m/s.