Abstract: In recent years, H₂S as a novel biomarker for asthma and chronic obstructive pulmonary disease is of great significance to human health monitoring, so it is urgent to study H₂S sensors with low power consumption, high selectivity, low detection limit and high stability. Co(CO₃)_0.5(OH)·0.11H₂O/WO₃ nanomaterials were synthesized by a two-step in situ growth method. Different Co(CO₃)_0.5(OH)·0.11H₂O/WO₃ nanomaterials were grown in situ on WO₃ nanosheets by regulating the water bath reaction time using WO₃ nanosheets as a substrate synthesized by in situ hydrothermal method. The composites were characterized by FE-SEM, FTIR, XRD and TG, and then tested for gas sensing performance. The results show that the Co(CO₃)_0.5(OH)·0.11H₂O/WO₃ composite prepared after 20 min reaction has the best gas-sensitive property, and the response value to 50×10⁻⁶ H₂S gas at the optimal working temperature (90℃) is as high as 109. The response and recovery time are 130 s and 182 s respectively, showing excellent selectivity for H₂S gas. The composite still has a good response/recovery curve in low concentration H₂S (3×10⁻⁶) atmosphere. In three repeated tests conducted in one month, it showed good repeatability and long-term stability. The in-situ preparation of Co(CO₃)_0.5(OH)·0.11H₂O/WO₃ gas sensing materials and the study of gas sensing properties provide a new idea for the preparation of gas sensing devices and a new way for the diversity of gas sensing materials. It has potential application value in environmental detection and intelligent medical treatment.