The invention provides a carbon dot/chitosan detector with a dual detection function, which is established by an electrodeposition method. A preparation method of the carbon dot/chitosan detector with the dual detection function comprises the following steps: 1) preparing a carbon dot/chitosan compound electrodepositing solution; and 2) electrodepositing carbon dot/chitosan and establishing the detector. The carbon dot/chitosan detector is applied to dual-function detection. The carbon dot/chitosan detector has the advantages of simple preparation method, convenience in operation, mild preparation condition, easiness in control, simple equipment, energy conservation, environment friendliness, low cost and the like; the established carbon dot/chitosan detector has two detection functions of electrochemical detection and fluorescence detection at the same time, so that the effect of detecting some substances can be better achieved; and the carbon dot/chitosan detector has a good application prospect in the fields of detectors and biosensors.