Hot coal gas filtration using ceramic candle filters with off-line cleaning showed rapid changes in pressure loss and face velocity during filter cleaning, due to the injection of cleaning gas and the decrease of filtration area. These changes had the capacity to affect facilities which are sensitive to pressure change and filter durability. From this point of view, on-line pulse jet cleaning was thought to be preferable to offline cleaning but still caused some changes. Numerical calculations showed that a smaller system pressure loss before cleaning and a short pulse duration were most effective in reducing those changes. Some properties of the pulse jet cleaning were also investigated both experimentally and by numerical calculations. In a long candle, the cleaning pressure, which is the pressure difference in the filter and residual dust layer, varied along the filter, and a diffuser or an entrance region was necessary to accomplish cleaning throughout the filter. A one dimensional numerical model could estimate the cleaning pressure as a function of reservoir pressure, filter permeability, etc.