A piston ring assembly consists of an upper ring and a lower ring. Said upper ring and lower ring have a common axis, an outer toward common annular surface, and inner toward common annular surface and mutual contact surfaces. Said two contact surfaces keep to contact with each other in a contact section which has radially an outer end and an inner end. Said tow contact surfaces stretch radially oppositely from said outer end to form a first wedge space, the vertex of which being in the outer end and, with said outer toward common annular surface. The vertex angle is about 1030□. The distance between said outer end and said outer toward common annular surface is greater than the distance between said inner end and said inner toward common annular surface. The present invention also includes a piston wherein said piston ring assembly is being used.