Tunable diode laser absorption spectroscopy is a new trace gas detection technique provided with high precision in current. As the absorption of spectrum is popular for the advantages of high resolution, high analysis speed, non-contact detection and on-line monitoring, it has been widely applied in scientific research, industrial automation and other fields for gas monitoring techniques. In order to satisfy the requirements of accuracy and sensitivity with low concentration and the small signal noise ratio (SNR) of the trace gases for the instrument, it usually needs longer absorption optical path and complicated data processing algorithm which will surely increase the hardware and software costs of the analysis instrument. In this article, we propose an approach which utilizes the cooling and decompression effects of the high pressure gas when it is injected. With the detecting system hardware and software unchanged, we optimized the detecting system analysis capacity. For the installation of TDLAS detecting system where the sample gas inlet pressure is 0.3~0.5 MPa and exhaust pressure is 219.3 kPa, experimental results show that by using the jet vacuum enhanced method, we improved the signal SNR nearly 24 times, optimized the detection sensitivity almost to an order of magnitude and the precision increased 6.3 times.