In this paper, multilayer films Si/TiO2/Al2O32TiO2 and Si/TiO2/MgO2/TiO2 with thickness values from microns to tens of microns are fabricated by spin-coating method. The transmission spectra of these films are obtained by terahertz time-domain transmission spectrum system (THz-TDS). The phase shifts of reflection and phase penetration depths of Si/TiO2/Al2O32TiO2 and Si/TiO2/MgO2/TiO2 are simulated by the transfer matrix method. On this basis, two kinds of symmetrical THz microcavities each with a structure of DBR/LT-GaAs/DBR are designed and the radiation spectra are also simulated. The results show that the intensities of two microcavities are enhanced by 19 and 14 times at resonance wavelength, respectively. There are two resonance peaks in the emission spectrum of the structure Si/TiO2/Al2O32TiO2/LT-GaAs (12 μm)/TiO2/Al2O32TiO2, which are located at 208 μm and 248 μm, respectively. The reason is discussed based on the effective cavity length. The feasibility to regulate the emission properties of the THz source by introducing dielectric microcavities is discussed.