The intrinsic single mode fiber evanescent wave transmission characteristics and total power transmission are analyzed based on optical waveguide mode theory and fiber evanescent wave absorption principle. The sensor sensitivity formula is derived. Combining with sensitivity formula, the relationship among the sensitivity and the sensors’ geometric parameters, solution refractive index and the incident wavelength are investigated. The FD BMP is applied to the simulating process. The simulation results show that the core of the optical fiber sensing region is longer and thinner, the refractive index of the external solution is smaller, while the incident wavelength is shorter, the normalized output power is smaller, the sensitivity of the sensors is higher, which is consistent with the results of the theoretical calculations and the references reports. The results reported in this paper provide a reference for the study of the optical fiber evanescent wave absorbing sensors.