Optical gas sensing based on tunable diode laser absorption spectroscopy (TDLAS) has characteristics of high sensitivity and real-time response, but interferences and distortions may result in fluctuations and errors in the precious and stable measurement of gas concentration. Therefore, it is required to monitor and analyze parameters and waveforms throughout the TDLAS process. We propose and establish a visualized architecture with real-time interfaces and modules for the complete TDLAS process. It basically includes several functional modules, i.e., multiple frequency laser driving, operating temperature control, harmonic processing, and curve fitting, allowing elaborately in-situ monitoring the overall working status. The digital error amplifier based on type II compensation network for the proportional-integral-differential feedback controller was developed. Generated first and second harmonics and dual channel digital phase-locking algorithms were also developed in the TDLAS system. In the gas sensing experiment, the driving signal of the laser includes a 5-Hz triangular wave and a 1-kHz sine wave, and results show the favorable laser operating temperature variation of below ±0.02 ° C and the concentration calibration. The overall estimated measurement errors in the experiment are about 4.55% for the 300-ppmv gas. This visualization and in-situ monitoring system are helpful and universal for the optimization, calibration, and improvement of the TDLAS-related optical gas sensing.