Cr⁴⁺∶YAG crystal materials have been proved to be an ideal passive Q-switched material in recent years. Using MgO and CaO as sintering aid and charge compensation agent, 0.25% Cr⁴⁺∶YAG (molar concentration) transparent ceramics with high optical quality were successfully prepared by low-temperature vacuum sintering combined with hot isostatic pressing (HIP) sintering. Effect of MgO, CaO, and MgO-CaO co-added divalent oxides on the transmittance, absorption spectra, and fluorescent properties of Cr⁴⁺∶YAG ceramics were investigated. It is found that, compared with CaO and MgO-CaO series, MgO exhibits the most significant effect on the densification of Cr⁴⁺∶YAG ceramics when the vacuum-sintering temperature is 1 550 ℃. Especially when the molar concentration of MgO is 0.25%, the relative density reaches 98%. After HIP sintering at 1 680 ℃, the corresponding in-line transmittance of the densified Cr⁴⁺∶YAG ceramics reaches as high as 84.4% at the wavelength of 1 400 nm. Moreover, by annealing at 1 400 ℃ for 20 h, the absorption coefficient of Cr⁴⁺ at 1 030 nm reaches the highest value of 3.0 cm^-1, though some Cr³⁺ still remain in the Cr⁴⁺∶YAG ceramics.