A capacitance type gap sensor has been widely used in ultra-precision displacement measurement system. So far, voltage feedback measurement method has been applied to this type gap sensor, however, it has been accompanied with the complexity of electric circuit and noise problem. In this study, the gap information is acquired by using frequency mixing method for the purpose of providing solutions to these problems of voltage feedback measurement. The frequency mixing method extracts difference component between two frequencies, beating frequency, from modulated signals when two sinusoidal signals, which are very close in frequency domain, are mixed. This paper focuses sensor quality on high sensitivity, though measurement range is narrow. It is expected that this method will suggest a new way in view of sensitivity and linearity in place of voltage feedback measurement method.