Abstract: Symmetry method is a modern method in seeking conservation. A form invariance is a new symmetry. The paper studies the form invariance of differential equations of motion for holonomic systems in terms of quasi coordinates, under the infinitesimal transformations of groups. Definition and criterion of the invariance are given. The condition under which the invariance can lead to a conserved quantity is deduced. An example is given to illustrate the application of the result.