Joining steel and aluminum alloys is a common problem in many engineering structures. One of the alternatives for combining these materials is welding them using explosively welded transition joints. The biggest problem is the difference in welding temperatures of steel and aluminum alloys. The higher welding temperature of steel means there is a high risk of overheating the aluminum alloy in the transition joint. One of the methods of optimizing the dimensions of an explosively welded connector is to conduct experimental tests. These tests can indicate the minimum size of the connector in which the steel welding process does not cause changes in the microstructure and strength of the aluminum alloy. Conducting experimental research is time-consuming and expensive. First, it is necessary to produce explosively welded plates. Secondly, specimens of welded joints must be prepared. In order to minimize costs and speed up the design process, the number of experimental tests can be reduced by conducting numerical analyses. The aim of this work is to describe a method for modeling the distribution of temperature fields during welding of steel and aluminum alloy joints using transition joints. The method of manufacturing joint specimens and the method of experimental measurement of temperature during welding are described. The results compare the temperature distributions in an explosively welded connector during steel welding, determined experimentally and using numerical methods.