Modulation on electromagnetic waves with angle frequency ωe,travelling around a circular waveguide by high-frequency plane gravitational waves with angle frequency ωg,incident perpendicularly to the plane,where the waveguide is located,is discussed.Results present that in the vicinity of symmetric plane,perpendicular to the travelling direction of gravitational waves, of the waveguide,energy flux density of electromagnetic waves,generally will be added by three new components with angle frequencies(2ωe±ωg)and ωg,respectively.In the case as ωg》ωe,ratio-modulation of amplitude of energy flux density is as large as h0, the dimensionless amplitude of the gravitational wave,in order.Specially,when for ωg,ωe and ω0,the cyclical angle frequency of electromagnetic waves around the waveguide, ωg=2ωe》ω0 is satisfied,energy flux density will be greater than h0 in order because of some mechanism,similar to resonance.The results don't vanish when these parameters have a small change.It is very important to detect the very weak signals of gravitational waves.