Abstract: Conformal invariance and conserved quantity of Mei symmetry for Tzénoff equation in unilateral holonomic constraint system have been studied in the paper.First,the definition and judgment equation of Mei symmetry have been presented.The definition and judgment equation of Mei symmetry conformal invariance have been further explored and the relation between them has been analyzed.The conditions of conserved quantity for Tzénoff equation in unilateral holonomic constraint system have been researched as well.Finally,the condition equation and specific form of conserved quantity have been deduced.