The invention provides a laser-raman spectrum gas analyzer. The laser-raman spectrum gas analyzer comprises a laser, an optical resonator, a hollow reflection pipe, a scattered light collecting device and a spectrograph. The laser emits laser beams to the optical resonator. The optical resonator is composed of optical resonator reflectors. The hollow reflection pipe is a hollow pipe containing gas to be analyzed and is placed between two of the optical resonator reflectors in the optical resonator, and the laser beams in the optical resonator enter the hollow reflection pipe from one end and are emitted out through the other end of the hollow reflection pipe. The laser beams in the optical resonator transmit in the inner wall of the hollow reflection pipe and act with the gas molecules to be analyzed in the hollow reflection pipe to produce scattered light; the scattered light is reflected by the pipe wall in the hollow reflection pipe for multiple times and then are emitted out from the two ends of the hollow reflection pipe. According to the laser-raman spectrum gas analyzer, the cavity length of the optical resonator is precisely adjusted through piezoelectric ceramics, an external incident laser beam longitudinal mode is locked, and enhanced laser beams are formed in the optical resonator; the enhancing effect is dozens of times or higher that of a pure optical resonator enhancing technology, and the sensitivity of gas detection is improved.