Abstract: A filter assembly of an air filter, which includes a corrugated filter sheet, and both ends thereof are mounted in a clamp space between two rows of corrugated positioning grooves of the upper and lower clamp plates of a horizontal lintel; both sides thereof are clamped in two vertical jambs respectively; the corner ends of the horizontal lintel and the vertical jamb are connected together by using a connection plate to plug therein; then, the outer surface of the filter assembly and the corner ends will be pressed and punched to have the horizontal lintels, the vertical jambs, and the filter sheet fastened together to form into a filter for screening dust.