Abstract: For the heat transfer problem and the optimization of the furnace temperature profile in the reflow soldering working process, the corresponding model was established using the heat conduction law. Firstly, by analyzing the heat flowing into and out of a micro-element in the reflow oven, the variation of ambient air temperature in the oven is obtained. Then the heat transfer model in the PCB is established by combining the heat conduction equation with the relevant constraints. In this way, the whole PCB motion process is divided into five stages by combining the fact that parameters vary with temperature, and the conduction influence factor and convection radiation superposition influence factor are searched and solved according to the experimental data of different stages. The temperature variation in the center of the soldering area is obtained using the finite difference method. In order to determine the maximum over-burner speed as well as to design the furnace temperature profile, a variable-step search algorithm is designed in this paper.