Diamond is a kind of extremely functional material, which is widely used in the fields of industry, science and technology, military defense, medical and health, jewelry, and others. However, its application in the semiconductor field is still limited, because its electrical transport performance has not yet met the requirements of semiconductor devices. In order to improve the electrical transport performance of diamond as much as possible, the synthesis of diamond single crystal is studied by adding B₂S₃ to the synthesis system using temperature gradient growth (TGG) method at a pressure of 6.5 GPa in this work. The growth rate of the synthesized diamond crystal decreases from 2.19 mg/h to 1.26 mg/h, indicating that the growth rate of diamond is dependent not only on the growth driving force, but also on the impurity element in the synthetic cavity. Additionally, with the increase of additive dosage, the color of the synthesized diamond crystal changes from yellow to baby blue . Raman measurement results indicate that the obtained diamond appears as a single sp³ hybrid phase without the sp³ hybrid graphite phase. However, the corresponding Raman characteristic peak of the as-grown diamond crystal is located at about 1331 cm^–1 and tends to move towards low wave number. According to Fourier Transform Infrared Spectrometer (FTIR) measurement results, the absorption peaks at 1130 cm^–1 and 1344 cm^–1 are attributed to nitrogen defects. It is found that the nitrogen defect concentration of the synthesized diamond crystal decreases gradually from about 300×10^–6 to 60×10^–6. Furthermore, the electrical transport performance of the synthesized diamond is characterized by Hall effect measurement. Diamond has insulating properties due to the absence of any additives in the synthetic cavity. However, the results indicate that when B₂S₃ is introduced into the synthetic system as additive, there is almost no difference in carrier Hall mobility, but the difference in carrier concentration is as high as two orders of magnitude. Furthermore, the resistivity of the synthesized [111]-oriented diamond crystal decreases to 45.4 Ω·cm, due to the addition of B₂S₃ to the synthesis system. However, it is worth noting that the resistivity of the diamond crystal synthesized with 0.002 g B₂S₃ and Ti/Cu additives in the synthesis system drops sharply to 0.43 Ω·cm. Therefore, the nitrogen defects in diamond will have an important effect on its conductivity. It provides an important experimental basis for applying diamond to semiconductor field.