Abstract: Abstract: A photoelectric detection method based on paper-based microfluidic chip in pesticide residues is proposed because the existing equipment has the problems of high cost, low degree of automation and large amount of reagent consumables. We design a kind of simple, portable, inexpensive paper-based microfluidic chip, whose bridge composite structure can enhance the uniformity of the color reaction of microfluidic enzyme, and also design the light path and circuit structure suitable for optical absorption reflection detection. The signal amplifying circuit and filter circuit are built to eliminate the interference of clutter and noise in photoelectric detection. Finally, a portable detection system of pesticide residue is established, which is an integrated test platform of the chemical reaction, the reflection effect in light absorption and the control of environment parameters. We observe and optimize the light source, chip placement angle, temperature and other process parameters of test platform in Jiangsu University in 2016. The reflection absorption effect of red LEDs (light-emitting diodes) is tested to be the best among the LEDs with different colors through detecting the paper-based chip color area. The response effect of the system is better when the angle is 10 according to the chip placement angle and reflected voltage data of photoelectric detection during the reaction. It is concluded that light absorption is the most under 35 ℃ and the chemical reaction is the most sufficient via comparing the color effect of the biochemical reaction of enzyme inhibition under different temperatures. We design different concentrations of pesticides, which are used for biochemical reactions of enzyme inhibition in different paper-based microfluidic chips. The resulting product displays blue color region in the paper-based chip, which can be characterized by the color of the different concentrations of pesticides. We use the photoelectric detection device to detect the color zone of the chip; the reflected voltage data can be obtained with this method, which correspond to different concentrations. Based on the experimental data, the model is established by the reflected voltage and the concentration of pesticide. The pesticide residues of test samples can be analyzed quantitatively based on the detection model. It can be concluded from the experimental results that with the method of photoelectric detection, the minimum detection limit of pesticide residues (trichlorfon and parathion) can reach 0.05 mg/L, meeting the national standard, and the resolution can reach 0.002 mg/L, much higher than that with the traditional method. Within the concentration range of pesticide residues, compared with the pesticide residues detector and the rapid detection card, the detection limit for the photoelectric detection is equivalent, but the consumable items are respectively 5.21% and 41.7% of the former 2 methods, and the reduction of time is respectively 23% and 33%. We propose a kind of pesticide residues detection system, which combines the photoelectric detection system and the paper-based microfluidic chip, and possesses the advantages of easy integration and low consumption. The research provides the theoretical basis and realistic foundation for making the pesticide residues detection develop to be portable and universal.