The invention discloses a lower tube socket with a function of filtering foreign matters. The lower tube socket comprises a plurality of blades having mutually paralleled axles and a plurality of fillet assemblies having mutually paralleled axles, the axles of the fillet assemblies are vertical to the axles of the blades; the fillet assembly is composed of two symmetric fillets, the opposite faces of the two fillets are respectively provided with clamping slots having number corresponding to that of the blades, the blades are clamped in the clamping slots; the blade comprises a plurality of bulges having the same convex directions, two adjacent bulges are connected by a straight section, the upper end surface and the lower end surface of the straight section are provided with grooves, the opening direction of the groove is vertical to the convex direction of the bulge, and the fillet assembly is clamped in the groove. The lower tube seat disclosed by the invention is good in structure strength, filtering ability and coolant pressure drop.