Based on the theory of Fabry-Perot cavity, the resonant characteristics of microcavity structure are studied, which is formed by reflectors composed of two slabs of the same single-negative materials. If the reflectors are composed of ε-negative (ENG) material, the omnidirectional transmission of TM mode can be realized under certain conditions; for the case of μ-negative (MNG) material, the omnidirectional transmission of TE mode can be realized. The omnidirectional transmission spectrum narrows and quality factor increases with the increase of incident angle. The increase of the refractive index of material in cavity effectively reduces the size of microcavity structure for omnidirectional transmission of TM mode, but the modulation is less obvious for that of TE mode. The existence of single-negative material loss does not break the characteristics of omnidirectional resonance of two microcavity structures, but the transmissivity of resonant mode reduces with the incident angle. Through optimized processing, the conditions are found for these two types of microcavities to realize the omnidirectional transmission, which provides useful theoretical guidance to the design of omnidirectional filters.