This paper presents a new analytical method to study the dynamic coupli ng feature of a vibrating system driven by two motors with the same rotation dir ection. By introducing two variable parameters into the average angular velocity of the two exciters and their phase difference, a concept of torque of frequenc y capture is put forward after dimensionlessly processing parameters of the syst em and an equation of frequency capture of the system is deduced. The problem of synchronization is converted into that of existence and stability of zero solut ion to the equation of frequency capture. The computer simulation results show t hat the system can realize stable selfsynchronous operation state when the par a meters of the system meet the demands of frequency capture and that of stable se lfsynchronous operation. The simulation results verify the correctness of the theoretical analysis.