Planetary gear mechanisms are widely used in automobile automatic transmissions. However, the relevant design theories are not well development, especially the synthesis of the clutching sequence. Thus, the purpose of this study is to develop a systematical methodology for the design of automobile automatic transmissions. First, the specifications are established according to the characteristics of the automatic transmissions. Second, a procedure is created to list the speed ratio table and the clutching table for the planetary gear mechanisms. Third, based on the clutching table, a systematical method is developed to synthesize the clutching sequences. Then, the clutches and brakes are arranged into the planetary gear mechanisms to form the schematic of an automatic transmission. Finally, according to the relations between speed ratios and the numbers of teeth of gears, the gear-teeth synthesis is carried out when several certain speed ratios are assigned. A seven-link 2-DOF Ravigneaux gear mechanism, a eight-link 2-DOF Ravigneaux gear mechanism and a nine-link 2-DOF stepped Ravigneaux gear mechanism are as the design examples. And a four-speed, a six-speed and an eight-speed automatic transmissions are synthesized, respectively. The result of this study shows that the proposed methodology can be applied to design any 2-DOF planetary automatic transmissions.