A π-polarized (π-pol) 1084 nm laser based on Nd:MgO:LiNbO3 crystal under modulation pulsed pumping mode was demonstrated. The anisotropic Nd:MgO:LiNbO3 slab crystal was end-pumped by a pulsed laser diode (LD) with a different duty cycle for experiments. The dual-wavelength fundamental laser emission range was effectively controlled within a certain pump peak power interval, and the unmatched polarized fundamental laser is completely suppressed when the duty cycle is 20 % and below. At a repetition frequency of 5 Hz and pulse width of 40 ms, the π-pol 1084 nm fundamental laser with a maximum average output power of 1.396 W in the whole pump range was obtained, and the single pulse energy was 279.2 mJ.