The invention relates to multichannel fluorescence test system and method of a water concentration field. Adopting the principle (LIF) (laser induced fluorescence) that a tracer can generate fluorescence under the irradiation of a specific light source, the system includes: a tracer, fluorescein sodium, put in a water area, and probe groups set at each detecting spot in the water area. The probes are connected to collection boxes through shield cables, and the collection boxes are then connected to a central measurement and control computer equipped with collection and calibration software through a computer bus or communication network for conducting sampling, analysis and display on the tracer concentration of discharged sewage in a large water area. The important components, probes, include LEDs (light-emitting diodes) irradiating water currents containing the tracer, and photocells for receiving excited fluorescence in the water. The system and method of the invention fill the gap in the detection field of pollutant concentration fields in large water physical model experiments, and are also effective means for field observation of water pollution.