A smartphone digital colorimetric method was proposed for the rapid detection of sulfonamides based on the aptamer/AuNPs complexation structure.Aptamers were bound on the surfaces of AuNPs by the electrostatic interaction which changed the charge density of the nanoparticles surfaces and the complexation of AuNPs with aptamers，preventing the nanoparticles from aggregating in a high salt solution.The solution kept a stable red.In the presence of sulfonamides，the weaker binding between aptamers and the AuNPs was broken，and sulfonamides bound up with aptamers.The specific and stronger binding between sulfonamides and the aptamers led to the separation of the aptamers from the surfaces of the nanoparticles.The nanoparticles began to aggregate，which could result in a color changed from red to purple-blue.In order to achieve a precise，quantitative，fast and convenient detection，a smartphone was arranged to capture the digital images.The complementary wavelength of images was analyzed by a smartphone App，and the concentration of sulfadimethoxine（SDM） in the range of 0-5 μg/mL could be determined by analyzing the correlation between SDM concentration and the complementary wavelength.The method showed high sensitivity，and the detection limit was 013 μg/mL.