The oscillating frequency range of quartz crystal at basic oscillator circuits is analyzed and the critical frequency is introduced.It is shown that the oscillating frequencies of the three basic oscillator circuits Iie between the series resonance and the critical frequencies of the crystal

and generally it cannot be oscillated on. the parallel resonance frequency of the crystal.General formulas of the oscillating frequencies of the three basic oscillator circuits and the required transconductance of the tube are given.Finally

the ideal oscillating range is discussed and it is thought that the frequency stability of any types of oscillator increases as the oscillating frequency approaching to the series resonance frequency of the crystal.