The invention discloses a plate heat exchanger equipped with an on-line backwashing device. The invention belongs to heat-exchange equipment and particularly relates to a plate heat exchanger equipped with a washing device. The plate heat exchanger equipped with the on-line backwashing device is provided with a backwashing pipeline for communicating the primary side and the secondary side of the heat exchanger and a corresponding control valve to ensure that the primary heating medium reversely enters the secondary side, the secondary heating medium reversely enters the primary side, dirt between plates of the heat exchanger is washed and discharged through the reverse flow and the on-line dirt washing and discharging of the plate heat exchanger are realized, so that the work efficiency of the equipment can be improved and the washing cost is reduced.