Phasor measurement unit (PMU), which could provide high-frequency phasors including the amplitude and phase angle synchronized with GPS/ BDS signal, plays vital role in dynamic monitoring of power system. However, if the GPS/BDS signal could not be received, the time of PMU, which is depending on the crystal oscillator, would have a deviation due to the frequency deviation of crystal oscillator (FDCO). This paper analyzes and deduces the impact of constant FDCO on PMU measurement in steady state. First, the phasor measured by the PMU with constant FDCO in the steady state is derived. Then, the detailed analysis of the impact of the FDCO on the PMU measurement is carried out, when the value of FDCO is small and large. Finally, the impact of FDCO on angle and amplitude data of PMU measurements are verified with simulation, when the FDCO is small and large, respectively.