Hexavalent chromium detection in medicine capsules is generally analyzed in the laboratory, it is difficult to meet the demand for field detection, and to address this problem, a sensor which can be used for on-site detection of trace amounts of hexavalent chromium was designed. It mainly includes chemically sensitive materials, optical sensing module and signal processing module, the chemical sensitive materials is to achieve the conversion of the hexavalent chromium concentration signal, the optical sensing module is to complete a stable output of the laser light source, and the signal processing module is to complete a photoelectric conversion of the weak fluorescence signal, signal amplification, and data processing and displaying. With using the indigenously developed photoelectric acquisition, conversion and signal processing system to complete the rapid detection of trace amounts of hexavalent chromium, so the miniaturization of testing instruments and on-site detection were achieved. Experimental results show that: the sensor detection results have a good linear relationship when the hexavalent chromium concentration is 10～500 μg·L-1, the linear equation is Y=1.542 47*X－2.353 47, and the linearity is 0.998 62, the detection limit reaches 10 μg·L-1, the sensor response time is about 90 seconds, 5 capsule samples were selected to do the contrast detection, and the results show that the sensor quantitative detection data is reliable, which meets trace hexavalent low cost, fast and field detection demands.