The unified symmetry of a nonholonomic system of non-Chetaev’s type in event space under infinitesimaltransformations of group is studied.Firstly,the differential equations of motion of the system are given.Secondly,thedefinition and the criterion of the unified symmetry for the system are obtained.Thirdly,a new conserved quantity,besides the Noether conserved quantity and the Hojman conserved quantity,is deduced from the unified symmetry of anonholonomic system of non-Chetaev’s type.Finally,an example is given to illustrate the application of the result.