Abstract: Steam heating system in annulus is suitable for the production of high pour-point and high viscosity oil. A mathematical model of temperature field around borehole was established based on energy persistence theory, which was a normal differential and non-linear equation group under the condition of half-consealed edge. Depth of zero steam quality is calculated by iterative method firstly, and then the simple analytical solution of the model is derived. In addition, this paper presents an optimization model of injection parameters by a genetic algorithm with constraints, in which the least cost is taken as objective, restriction of wellbore temperature not lower than inflection temperature is taken as constraint condition. An application example was in Binnan oil production plant of Shengli Oilfield. The results show that the temperature model fits the field data well, and parameters optimization method is novel and fast. This model provides a new method for solving steam injection temperature field in annulus accurately and optimizing injection parameters rapidly.