The propagating characteristics of all-dielectric dual-cavity Fabry-Pérot (F-P) structure are studied by the method of transfer matrix,and the general expression of transmittance is also deduced. There are found twelve patterns of combining dual-cavity Fabry-Pérot structure which can produce resonant modes in the band gap,with requirement that the number of dielectric layers between two cavities must be less than the total number of dielectric layers outside the cavities. The first-layer media contacting with F-P cavity must be heterogeneous material when the optical thickness of F-P cavity is odd multiple of quarter-wavelength,otherwise they must be homogeneous ones when the optical thickness is even multiple. When two cavities are fixed in length,the position of resonant modes depends on the number of dielectric layers between two cavities,while the line width (FWHM) relies on the number of dielectric layers outside cavities. When the dual-cavity Fabry-Pérot structure is exactly symmetrical,the transmittance of both resonant modes equals 1.