Because conventional degasser and gas collector can not meet the requirements of the observation for small flow and low water head of gas volume, the quality of the chemical gas observation is directly affected. Taking Songshan spring radon-gas an example, we combined with the observation conditions of the station, through technical transformation and experimental research, and made a constant current splash off gas gathering device. Then, we conducted continuous radon observation, and obtained a complete annual dynamic change curve. The result shows that this new device can solve the instability problems of flow, gas quantity and water quantity in small flow and low head observation springs, and improve the stability of gas radon observation significantly. Our results provide an example for the technical improvement of other small flow and low head observation springs in earthquake fluid observation stations.