To solve increasingly serious food safety problems, especially the rapid detection of food-borne viruses, an E. coli sensor based on the surface-modified graphene enlarged-cone Mach-Zehnder interference structure was proposed in this study. First, a 4 cm solid photonic crystal fiber was intercepted and coarsely fused with two single-mode fibers to form an interference structure based on the Mach-Zehnder principle. Next, surface-modified graphene sensitive material was prepared. The modified graphene, coated on the surface of the solid photonic crystal fiber, allowed the sensor to have a higher sensitivity to E. coli solutions. Finally, the above sensor is placed in a water tank to detect the concentration of the E. coli. The experimental results show that the interference spectrum of the sensor has a significant blue shift with a sensitivity of 3.43 pm/(cfu·mL-1) in the range of 50-600 cfu/mL of the E. coli solution. The linearity between the bacterial concentration and wavelength shift is 0.956 49, detection limit is 67.18 cfu/ml, and response time is 15 s. The sensor has low cost, small volume, fast response time, and is suitable for the rapid detection of low concentration E. coli.