Large grained synthetic diamond single crystals have been synthesized by international advanced six-sided top hydraulic press by Ji’nan Zhongwu New Material Co. Ltd. To characterize the quality of these synthetic diamonds and establish the identification principles, 225 large colorless, yellow, and blue HPHT synthetic diamonds produced by the company were studied by stereoscopic microscope, multi-spectral induced luminescence imaging system (GV5000), infrared absorption spectrometer (FTIR), diamond photoluminescence spectrometer (PL5000), laser induced breakdown spectrometer (LIBS) and X-ray energy dispersive spectrometer (EDS) and compared to natural diamonds. The crystal morphology of HPHT synthetic diamonds is mainly composed of octahedral (111) plane and cubic (100) plane. The yield rate of the round bright cut diamonds is between 20% and 67%. The clarity grades of colorless HPHT synthetic diamonds range from VVS to P, and color grades are between D to H. GV5000 is employed to perform a study of both growth structure and luminescence characteristics of the samples. The cubic-octahedral luminescence patterns related to crystal growth structure can be observed in all samples of three colors. The colorless samples show strong blue fluorescence and phosphorescence. The luminescence peak is at 495 nm, which is related to the paramagnetic nitrogen in the lattice. The blue samples show blue to greenish blue fluorescence and blue phosphorescence, with the luminescence peak at 501 nm, related to the paramagnetic nitrogen and boron in the lattice. The yellow samples show weak green fluorescence and phosphorescence and the luminescence peaks related to Ni+ are at 556 and 883 nm. Synthetic diamonds with those features above can be distinguished from natural ones. Infrared absorption spectra show that the colorless HPHT synthetic diamonds having no significant nitrogen-related absorption at 1 332~1 100 cm-1, with boron (B0) related absorption at 2 802 cm-1, are classified as type Ⅱa containing a small amount of boron. The blue HPHT synthetic diamonds are type Ⅱb with strong boron-related absorption at 1 294 cm-1. The yellow HPHT synthetic diamond samples are type Ⅰb with obvious absorption peaks at 1 130 and 1 344 cm-1 which are caused by single nitrogen. Luminescence peaks related to Ni defects at 659, 694, 708, 714 and 883 nm are observed in colorless, blue and yellow samples under photoluminescence spectra (PL5000). In contrast, natural colorless and yellow diamonds are usually type Ⅰa, with infrared absorption peaks at 1 282 and 1 175 cm-1 caused by aggregate nitrogen. Zero phonon lines at 415 nm (N3) can be detected by photoluminescence spectra. Spectral features caused by isolated nitrogen, boron and nickel are extremely rare in natural colorless and yellow diamonds. Therefore, infrared absorption spectra and photoluminescence spectra features can be used as the significant evidence for identification. The main composition of the extrusive inclusions in colorless HPHT synthetic diamonds turns out to be Fe by LIBS. EDS analysis displays that among samples with a relatively large number of inclusions, Fe is detected in blue and colorless samples, and Fe and Ni are tested in yellow samples. Both Fe and Ni are compositions of inclusions, which can be used as one of the identifiable characteristics of HPHT synthetic diamonds. In conclusion, the large grained HPHT synthetic diamonds can be distinguished from natural diamonds based on the fluorescence and phosphorescence characteristics under ultra-short ultraviolet light irradiation (GV5000), accompanied by infrared absorption spectra, photoluminescence spectra (PL5000) and X-ray energy dispersive analysis features.