The most significant advantages include multi-component, noncontact detection, short testing period and molecular fingerprint characteristics. Raman spectroscopy has been successfully used in many fields. However, the low Raman-scattering signal limits its further development. In order to improve the sensitivity of Raman liquid detection, a method for enhancing the liquid Raman signal based on a new sample cell is reported in this paper. A concave mirror is added to the bottom of the traditional cuvette. On the one hand, the laser can be reflected and focused again after acting on the sample. On the other hand, the Raman scattering signals of forward and backward are collected by the setup at the same time. Thereby the Raman signal can be improved. Firstly, the influencing factors of Raman scattering intensity and the relationship between the Raman scattering signal intensity and the collection angle excited by unpolarized light are analyzed theoretically. It is concluded that the scattering intensity is the largest when the collection angle is forward and backward (0° or 180°). A new sample cell was designed, and the silver-plated concave mirror (diameter 12.5 mm, focal length 10 mm) and quartz tube (outer diameter 12 mm, wall thickness 1 mm, length 30 mm) was bonded with UV glue to form a liquid sample cell. A 785 nm Raman probe setup was used to conduct relevant experimental research, and different samples (75% ethanol, isopropanol, methanol) were detected and compared with traditional cuvettes. The results showed that the new sample cell is effective for different liquid samples, and the detection sensitivity can be improved, the enhancement factor is nearly 4 times. In order to analyze the repeatability of the new sample cell manufacturing method, the detection effects of the three sample cells were compared in the experiment. Lastly, to verify the detection ability of low-concentration samples, the 75% ethanol solution diluted 20 times was detected using the new sample cell. The result shows that the new sample can obtain effective Raman spectroscopy information. The experimental results prove that the new sample cell can improve the detection sensitivity of liquid Raman spectroscopy. It has a simple structure and a wide range of applications.