Through controlling the laser waveform of the two-color field, the selective enhancement of single-order harmonic is obtained theoretically. The theoretical analyses show that the selective enhancement of single-order harmonic is attributed to the folded region of the harmonic emission process in a specific 'W' waveform. Moreover, the folded region in the 'W' waveform structure is very sensitive to the pulse duration of the second controlling pulse. The present investigation provides a new method to obtain the single-order harmonic, which is helpful to the development of the laser source.
