The third harmonic generation of the super intense ultrashort pulse with a single β-barium borate (BBO) crystal was studied theoretically and experimentally.The effects of the intensity of the fundamental field,the thickness,the detuned angle and the azimuth angle of the crystal on the conversion efficiency and the pulse shape were analyzed.The parameters of the experiment were optimized.The corresponding experiment was performed for the ultrashort pulse with center wavelength of 810 nm,the pulse width (FWHM) of 100 fs,the bandwidth of 25 nm and the pulse energy of about 6 mJ by using a single BBO crystal.The conversion efficiency of the third harmonic generation can approach 0.8%.Analyzing the experimental results,we proposed the methods for improving the conversion efficiency of the third harmonic generation with a single BBO crystal.