Abstract: On a new experimental set-up of filter with three ceramic filter elements, the transient velocity outside the filter element is measured by hot-wire anemometer during pulse-jet cleaning process. The influences of reservoir pressure and pulse duration on instantaneous velocity are investigated. The experimental results show that there exists a remarkable back-flow between the pulse-jet cleaning and normal filtration process. It is shown that the pulse-jet cleaning velocity and back-flow velocity increase with rising reservoir pressure. The back-flow velocity peak is several times of filtration velocity and makes fine particles redeposit on the filter element surface and even penetrate the filter element wall.