The invention provides a detector and a detection method. The detector includes an optical transmission device, a fiber detector, a collecting device, and a signal processing module. The optical transmission device is configured to transmit light emitted by a light source to the fiber detector and transmit the light outputted by the fiber detector to the collecting device. The fiber detector is configured to transmit light entering the fiber detector to a reflector and transmit light reflected by the reflector to the optical transmission device. The fiber detector includes a fiber having at least one portion of the core exposed; the exposed core is used for installing an indicator film; and the indicator film can react with a to-be-detected object to change the refractive index so as to change transmitted wave spectrum of the fiber detector. The collecting device is configured to collect the light outputted by the optical transmission device, convert the electrical signal into an electrical signal and transmit the signal to the signal processing module. The signal processing module is configured to compare the electrical signal with a pre-stored electrical signal to determine to-be-detected data of the to-be-detected object. The detector has advantages of high measurement precision, strong anti-interference ability, simple measurement process, and fast data display speed and the real-time measurement of to-be-detected data is realized.