Currently, the determination of room-temperature gas-sensing performance is primarily based on the method of collecting and analyzing the electrical signals generated after gas interacting with sensitive materials. However, we found that there are Raman characteristic peaks associated with gas sensitivity in the in-situ Raman tests, which is considered as a favorable voucher for evaluating gas-sensing performance. Moreover, in-situ Raman spectroscopy is a non-destructive analytical technique for in-depth understanding of the chemical structure, changes in bonds under atmosphere, etc. of materials. In this study, in order to investigate the Raman signals of the sensitive materials under room-temperature ammonia (NH3) atmosphere and evaluate its gas-sensing performance, the nanocomposites of tungsten disulfide (WS2) nanosheets (NSs) decorated by platinum (N) quantum dots (QDs) were prepared by in-situ hydrothermal method for in-situ Raman spectroscopy tests under room-temperature NH3 atmosphere. The Raman spectrum results show that there is the characteristic peak at 1328 cm(-1), and the peak intensity ratio of the characteristic peak to the strongest Raman peak of WS2 NSs shows an approximately linear with the concentration of NH3, and behave good stability and selectivity to NH3. Furthermore, the effective area percentage of N QDs loading on WS2 NSs is approximately linear with the theoretical molar ratio of N to WS2, indicating that the theoretical molar ratio and the actual effective area percentage to the peak intensity ratio are consistent. The in-situ Raman technique under atmosphere could provide a direction for evaluating room-temperature gas-sensing performance.