The invention provides a detection device and an optical system thereof, wherein the optical system comprises a laser, at least one diaphragm, a reaction container, a transmission photoelectric sensor and at least one scattering photoelectric sensor, wherein the laser is used for transmitting laser; the at least one diaphragm, the reaction container and the transmission photoelectric sensor are arranged in sequence along the optical axis of the laser; the transmission photoelectric sensor is used for detecting the light intensity of transmitting laser through the reaction conditioner; the at least one scattering photoelectric sensor is used for detecting the light intensity of scattering light through the reaction conditioner; an optical channel of the scattering photoelectric sensor and the optical axis of the laser form an included angle more than 0 degree but less than 180 degrees. The optical system provided by the invention has the advantages that transmission turbidity detection is realized, and simultaneously at least one scattering photoelectric sensor is also arranged and is used for detecting the transmission turbidity; due to higher sensitivity and accuracy of transmission turbidity detection, the defect of transmission turbidity detection can be made up.