Food safety has attracted public attention because of pesticide residue contamination. It has certain theoretical and practical significance to develop fast, accurate and highly sensitive new methods for detecting pesticide residues. In this paper, a colorimetric and fluorescent dual-mode optical sensor has been designed for sensitive detection of pesticide residues by using the difference of plasma absorption spectrum of aggregation and dispersion gold nanoparticles and the internal filtration effect between fluorescent molecule rhodamine 110 and gold nanoparticles. Gold nanoparticles (AuNPs) with a diameter of about 13 nm and a negative charge on the surface were synthesized by the citrate reduction method. They were dispersed in an aqueous solution and showed wine red. The maximum absorption wavelength of the solution was 520 nm. Pesticide molecules can induce the aggregation of dispersed AuNPs by forming Au-N or Au-O coordination bonds, resulting in the color changes of the solution gradually from redwine to blue-purple. Pesticide content can be detected according to the change of absorbance of the solution at 520 nm. The significant color change of the solution can be observed even with the naked eye. The detection method has the advantages of simplicity, rapidity and low cost. Although the single colorimetric detection mode is simple, false positive is possible. In order to further verify the accuracy of the results and improve the detection sensitivity, fluorescent dye rhodamine 110 with the positive charge is introduced into the dispersed AuNPs solution, which can adsorb on the negatively charged AuNPs surface. In this state, the AuNPs are still well dispersed in the solution. The fluorescence spectrum of rhodamine 110 overlaps with the absorption spectrum of AuNPs, leading to the fluorescence internal filtration effect (IFE). The fluorescence intensity of the solution is very weak, even with no fluorescence emission. In the presence of pesticide molecules in the solution, they compete for adsorption with the fluorescent dyes on the surface of AuNPs to induce the aggregation of AuNPs. The color of the solution changes from redwine to blue purple. At the same time, the fluorescence of rhodamine 110 molecules released into the solution is restored. The colorimetric and fluorescence dual-mode detection of the targets is realized according to the changes insolution absorbance and fluorescence intensity. As a model molecule, phoxim was used to test the sensors performance. The limit of detection for color imetry and fluorescence were 15.0 and 4.0 nmol·L-1, respectively. The test results of actual samples showed that the sensor had certain application potential in the food safety field.