The invention relates to an apparatus for filtering solid impurity in gas. The apparatus comprise a gas outlet housing, an inflation housing and a filter core, the inflation housing comprises a filtering housing and an inflation joint, a gap structure is existed at the external part of the filter core and between the filter cores, and the cross-sectional area of an inflation channel in the inflation joint is smaller than the cross-sectional area of a filter chamber in the filtering housing. The design structure can effectively buffer and reduce the flow velocity of the filled gas, so that the filter core has good filtering effect for filtering the solid impurity.