The invention provides a filter membrane filter element backwashing device and a backwashing method. The filter membrane filter element backwashing device comprises a backwashing adapter and a backwashing cap, wherein the backwashing adapter can be adaptively connected with a filter element water inlet end of a filter membrane filter element, and the backwashing cap can be adaptively connected with the filter element water outlet end of the filter membrane filter element; during backwashing, the backwashing cap is connected with the filter element water outlet end of the filter membrane filter element, the backwashing adapter is connected with the filter element water inlet end of the filter membrane filter element, and water enters the filter membrane filter element through the backwashing cap, and is discharged from the filter membrane filter element through the backwashing adapter. The backwashing method implemented by the filter membrane filter element backwashing device comprises the steps of pre-impregnation, backwashing, returning and the like. According to the device and the method, a backwashing technology can be used for efficiently and rapidly cleaning surface pollutants to recover the water flux and the filtering accuracy of the filter element with the recovery rate of more than 97 percent and prolong the service life of the filter membrane filter element of a water purification product.