Abstract: Mid-infrared laser at 3-5 m has very important application in opto-electrionic countermeasure. If the infrared laser is pico-second pulse, as it has much higher peak-power, it will be much more powerful in contermeasure filed. In this paper, tunable optical parametric generator (OPG) pumped by a 1.06 m picosecond laser based on periodically poled stoichiometric lithium tantalate (PPSLT) was reported to get pico-second mid-infrared laser. The periodically poled Lithium niobate crystal was a single structure (29.5 m). The pumping source was a home-made pico-second laser, which used a LD side- pumped regenerative amplifier. The maximum output power was 2.02 W at a frequency of 1 kHz, and pulse-wide was 13.6 ps. A continuous tunable middle-infrared (mid-IR) spectrum (idler wave) of 3.98- 3.68 m was obtained by changing the crystal temperature from 40 ℃ to 200 ℃. When the maximum available average pump power was 2.02 W, the idler output power of OPG was 190 mW at 120 ℃, the optical-optical efficiency was 9.4%. This experimental research shows the possibility to get a output of picosecond mid-infrared laser by OPG at several watts level.