The imposed interference by the signal electrodes limits the expansion of the measurement range in electromagnetic flow sensors (EFS). This is because the interference makes it difficult to increase the signal-to-noise ratio in the state of the microfluid. In this paper, an Ag/AgCl/porous graphite electrode sensor is successfully prepared by a chemical vapor deposition (CVD) method. This enables a high-reliability and wide measurement range surveillance system, which is also maintenance-free and cost-effective and has a long lifetime. AgCl is facilely synthesized by a mild method, and our analysis and experiments show that as-prepared AgCl nanoparticles demonstrate a high crystalline level and high quality. Further system testing and experiments are also conducted on EFS in cases where the Ag/AgCl/porous graphite electrode sensor is set as the core. It is seen that, within the flow range of 0.003-4 m3/h, the induced electromotive force is linearly related to the flow rate of the fluid. The measurement accuracy of the EFS using the transient measurement method is below 1%, and its sensitivity is not affected by the fluid temperature.