Insights into the mechanism of reflow soldering temperature curve, a mathematical model of the temperature change of the circuit board surface is established. The heat transfer methods, heat radiation and heat convection is analyzed in detail. The curve of air temperature inside the reflow furnace is solved by establishing an one-dimensional heat conduction model and fitting coefficients. The heat radiation received by the circuit board mainly comes from the small temperature zone. Depending on the area where the circuit board is located, heat radiation is itemized into 3 types: heat radiation in the gap, the temperature zone and the adjacent temperature zone of the area before and after the furnace. The impacts of heat radiation is weighted and analyzed by relative distance. For coefficients, analyzing and fitting is further discussed.