The invention provides a detection device for detecting the impurity in milk and a detection method thereof; the detection device comprises at least a conductivity detection unit, at least a temperature detection unit, at least a data processing unit and at least a display unit; the data processing unit can compare a measured conductivity value under a temperature value with the stored standard conductivity value to obtain a deviation value; when the deviation value is greater than the pre-stored deviation reference value, the data processing unit sends a first signal to the display unit; and when the deviation value is less than the deviation reference value, the data processing unit sends a second signal to the display unit. The device can simultaneously carry out automated inspection and monitoring on a plurality of production lines and various impurities, so as to effectively reduce the inspection time and manpower input; therefore, the device can be used for rapid online qualitative detection.