The invention provides an underground movable modular mine water treatment system which comprises the following steps: firstly, introducing mine water into a shaft sump for sedimentation treatment; carrying out solid-liquid separation treatment on the settled mine water to remove fine suspended solids therein; carrying out oil water separation treatment on first coarse purified water to remove dissolved oil and emulsified oil to obtain second coarse purified water; and carrying out ultrafiltration treatment on the second coarse purified water to remove organic matters therein so as to obtain purified water. The invention provides a device for treating mine water underground. The device comprises the shaft sump, a solid-liquid separation device, an oil water separation device, an ultrafiltration device and a control device. The system provided by the invention has an obvious effect for removing organic matters in mine waste water. The pollutant concentrations of the mine waste water treated by the system are obviously reduced, and the removal rate is relatively high. The device provided by the invention can be directly arranged in the coal mine and the mine water treated is directly reused in the pit, so that the investment and operating cost of waste water treatment are hugely saved.