Abstract: A Capacitance and condutance spectruometer has been established by using differential method. This measuring system is characterized high plecision and highly automatic automaticoperation.With this system a variation of capacitance as small as 0.01 pF can be measured.Another characteristic of the measuring system is that is can measure both the relative and absolute value of capacitance and conductance. The testing result shows that the preecision of this measuring system has reached that of the capacitance spectrometer from HP corporation, manufacture process of heterojunction and conjunction device fabricated on semiconductors can be studied.