Abstract: A 4-node quadrilateral quasi-conforming plane element with internal parameters was proposed under the framework of quasi-conforming technique. New displacement functions with internal parameters can be added to the serendipity element Q4 to construct new isoparametric element. The explicit stiffness matrix of quasi-conforming element QC6N makes it more efficient. The numerical tests and comparisons with other 4-node isoparametric elements suggest that the present elements are more accuracy and less sensitive to the mesh distortion.