The wide applications of terahertz (THz) wave technology in the ∼1-3 THz range has resulted in a surge in the demand for the performance improvement of THz wave detection technique. In this study, a frequency tunable, highly sensitive frequency upconversion detection based on a 2-(3-(4-hydroxystyryl)-5,5-dime-thylcyclohex-2-enylidene) malononitrile (OH1) crystal at room temperature is demonstrated. Moreover, to effectively increase the signal-to-noise ratio in the low frequency range, a beam isolation enhancer is proposed and its effect is verified. The minimum detectable THz pulse energy reaches about 100 aJ at 1.9 THz. The frequency tuning ranging from 1 to 3 THz. Sensitivity comparison with a 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal system shows that OH1 is a more suitable nonlinear crystal in the 1-2.4 THz range.