Pulse train control technique is realized through the output voltage regulation of switching dc-dc converter by adjusting the control pulse combination of high-power and low-power control pulses in a control pulse repetition cycle. Once the circuit parameters are determined, the control pulse combination is fixed. The control pulse combination directly affects the steady-state performances of pulse train (PT) controller. In this paper, the control pulse combination of PT control technique is studied by using the continued fraction technique. A one-dimensional normal form of discrete-time map of PT controlled buck converter operating in discontinuous conduction mode is also established in which the steady state performances, such as parameter evaluation of multi-periodicities and output voltage ripple of PT controlled DCM buck converter, are analyzed. The simulation result, experimental result, and the results in the literature are in accordance with the theoretical analysis. This investigation is helpful to obtain a deeper understanding of PT control technique.