Since the different conductivity of gutter oil and edible oil normally result in the different resistivity per unit volume, a linear detection module based on CMOS (Complementary Metal Oxide Semiconductor) was designed, which shorted to ground combined with directly selection the resistor string to divide voltage makes more linear precision voltage divider. Under the action of counting pulse, the count resistor divider compares with the reference voltage to achieve different number of high level, which not only can distinguish gutter oil and edible oil, but also come to the mass fraction of edible oil, which incorporates gutter oil. In the design of core circuit of detector, this detector is easy to achieve low area and low power base on CMOS.