In order to carry out the study of biological effect on dc superimposed low-frequency high-voltage pulsed electric field, a numerical control dc superimposed low-frequency high-voltage pulse generating device was designed. This device can generate dc superimposed low-frequency high-voltage pulse with stable dc high-voltage fundamental wave, wide pulse width and steep edge. The amplitude of dc high-voltage fundamental wave voltage is adjustable from 3 to 10 kV, the amplitude of pulse voltage is adjustable from 1 to 3.5 kV, the pulse frequency is adjustable from 1 to 100 Hz, and the pulse width is adjustable from 5 to 500 milliseconds. This device has advantages of simple structure, low cost and high dependability. Using the dc superimposed low-frequency high-voltage pulsed electric field with 350 kV/m of dc high-voltage fundamental wave, 75 kV/m of high-voltage pulse, 100 Hz and 5 milliseconds pulse width to treat aged cotton seeds with plate electrode, the results showed that: the four germination indexes of cotton after dc superimposed low-frequency high-voltage pulsed electric field treatment showed a trend of increasing. Under the 40 seconds treatment condition, the germination potential increased by 36.7%(P