The ultimate aim of the oil shale in-situ pyrolysis technology is to heat the oil shale to the state of pyrolysis. Direct heating, which can be realized by heating in the well to achieve the highest energy utilization rate with the smallest heat loss, has become the main heating way of the in-situ pyrolysis. In this paper, a new type of downhole heater with spiral baffle is developed, and due to the spiral continuos distribution, the contact time of gas and heating rod can be effectively prolonged to remarkably increase the heat transfer coefficient of heat rod surface. This paper also focuses on surface heat transfer characteristics of the in-situ pyrolysis heater with spiral baffle. Through the numerical simulation and theorecical deduction, the effects of the spiral baffle’s pitch and the gas mass flow on the heat transfer coefficient of the heating rod surface is analyzed, it is concluded that the smaller the pitch of the baffle or the larger the gas mass flow the higher the heat transfer coefficient of the heating rod; in the meanwhile, the fitting equations for heat transfer coefficient of heating rod surface changing with the pitch and gas mass flow are obtained to provide the theoretical support for the following-up design of the heater with spiral baffle.