Abstract: Based on the theory of ordinary open cavity emersion mode and waveguide mode,a new kind of mode lying between the liberty room mode and waveguide mode was studied,and the method of diffraction integral of Fox-Li in the area between the cavity mirror and the waveguide was used,the electric field was dispersed into every waveguide mode in the waveguide,by time after time alternating,the stabilization electric field in the space between the waveguide dimension and non-waveguide dimension was analied.Having the difference between the new mode,waveguide mode and Gauss mode,it is yalidated that the new electric distribution is similar to them,but a new electric field.