The invention discloses a water purification device, comprising a first pressure cylinder, a second pressure cylinder, a first connecting piece and a second cylinder block arranged successively from bottom to top, and further comprising a first cylinder block arranged inside the second cylinder block. The first pressure cylinder and the second pressure cylinder both are open at one end and formed with a first through-hole at the other end; the first cylinder block and the second cylinder block both are open at two ends and arranged in a hollow shape. A water inlet, which is communicated with first flow passages formed between the first cylinder block and the second cylinder block, is formed on the second cylinder block, and a water outlet pipe, communicated with the first cylinder block, is inserted into an outer wall of the water purification device. According to the water purification device disclosed by the invention, in case that an ultrafiltration membrane is required to be cleaned, the water flow is guided into the water purification device from a second through-hole, and the stains remaining in the ultrafiltration membrane can be flushed away under the action of the water pressure so as to prevent the ultrafiltration membrane from being clogged and scrapped due to accumulation of excessive stains, thereby greatly improving the service life of the ultrafiltration membrane and reducing the cost of water purification.