Noncritical phase matching (NCPM) fourth-harmonic-generation (FHG) experiments were conducted on different deuterium content DKDP crystals by adjusting crystal temperature to generate 266 nm deep UV laser. Specially, near room temperature NCPM is realized in extremely high deuterium content DKDP crystal at 38.6 °C, which is the lowest temperature to the best of our knowledge. NCPM temperature of DKDP crystals in 60-100% deuterium content range and 1050-1070 nm wavelength range are determined by a linear relationship according to the experimental and calculated results. Angular tuning properties are independent with deuterium content in medium and higher deuterium content DKDP crystals. All of these results will provide good references for future FHG applications of 1 μm laser with DKDP crystals.