The gas heater, reliable as it is, is nevertheless slow in getting started, and is one of the low-efficiency energy consumption equipments adopting the indirect heating by the intermediate heat carrier medium. Apparently, the form of heat transfer process of the intermediate heat carrier medium, i.e. the flow field organization in the large capacity cylinder, is one of the key elements that can improve the thermal efficiency of gas heater. Experimental investigation and analysis of the flow condition and temperature distribution between the water and ethylene glycol in the cylinder were carried out. Based on the investigations on medium selection and heater’s integral structure and combining with the engineering practical needs, effective measures to improve the efficiency of gas heaters have been brought forward in this article and the technology has got itself the China patents.