Hydrogen sulfide (H₂S) is widely found in oil and natural gas wells and industrial wastewater tanks. Owing to its high toxicity, the monitoring and detection of H₂S in the air is essential. However, recent techniques for the quantitative detection of H₂S gas suffer from limitations such as high cost, complicated operation, and insufficient sensitivity, preventing their practical application in industry. Thus, we have developed a portable test paper for real-time and inexpensive monitoring of H₂S gas by color changes. The test paper had a significantly low H₂S detection limit of 200 ppb, which is considered safe for humans. Moreover, the color of the test paper did not change noticeably when exposed to CO₂, N₂, O₂, and air environments, indicating that the test paper is selective for H₂S gas and can be stored for a long time. In addition, we fitted a color difference linear model between the color difference values (ΔE) and the concentrations of H₂S gas. The establishment of the linear model substantiates that the test paper can provide accurate intensity information when detecting H₂S gas leakage.