The invention provides a membrane distillation apparatus and a membrane distillation system possessing the membrane distillation apparatus. The membrane distillation apparatus comprises a shell, a hot-liquid bin arranged in the shell, a cold-liquid inputting bin, a cold-liquid outputting bin, a condenser pipe, an inner membrane and a pressure-adjusting mechanism; the cold-liquid inputting bin and the cold-liquid outputting bin are in communication via the condenser pipe, and the condenser pipe penetrates through the hot-liquid bin; the inner membrane penetrates through the hot-liquid bin and is sleeved around the condenser pipe, and a gap between the inner membrane and the condenser pipe forms a water-generating channel; and the pressure-adjusting mechanism is communicated with the water-generating channel and is used to adjust the pressure in the water-generating channel. By adjusting the pressure in the water-generating channel, a relatively large pressure difference is formed between the water-generating channel and the hot-liquid bin, and steam in the hot-liquid bin is promoted to relatively well penetrate through the inner membrane and enter the water-generating channel and be condensed, the membrane flux of the inner membrane is increased, the efficiency of the membrane distillation apparatus is improved, and steady running of the membrane distillation apparatus is guaranteed.