The invention provides a measurement device and a measurement method for the concentration of pollutants in water. According to the measurement method, a Q-modulating pulse laser signal is emitted by a passive Q-modulating fiber laser device and is transmitted by an evanescent field optical fiber, an evanescent wave is output to a to-be-detected water sample, and an output repetition frequency result of the passive Q-modulating fiber laser device is output based on the change of the evanescent wave caused by an absorption effect of the pollutants in the to-be-detected water sample to the evanescent wave and the change of an output repetition frequency of the passive Q-modulating fiber laser device caused by the change of the evanescent wave. The measurement method is simple, and the measurement device based on the measurement method is simple in structure and low in manufacturing cost.