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In this paper, the characteristics of time transfer using global positioning system (GPS)-smoothed P3 code and International GPS Service (IGS) precise ephemerides are studied. Recently, GPS P3 code has been used in International Atomic Time (TAI) computation as a substitute for GPS C/A code; however, this observation still has large variations when satellites are at low elevation angles. For acquiring more stable time comparison results, we adopt a carrier smoothing technique to reduce this noise. The IGS precise ephemerides are also used to reduce satellite orbital errors in order to obtain better results. To test our program for use in international time transfer, we processed GPS data between various laboratories using the smoothed P3 code and IGS ephemerides. We then compared these results to those obtained using unsmoothed P3 code and broadcast ephemerides. This test shows that using the smoothed P3 code and IGS ephemerides can reduce the uncertainty of GPS time comparison.