Abstract: The equation of electric-field distribution was established based on  the fundamental theories of waveguide structure and the resonance, and also the dispersion equation was obtained according to the boundary conditions and power-normalization. Furthermore, the sensitivities of surface plasma wave (SPR), long-range plasma wave (LRSPR) and reversible metal-cladding waveguide (RMW) etc three sensors, were derived from E_y/x. It is suggested that the sensitivities of three waveguides should be proportional to P_n/P_total