A new viewpoint is proposed for understanding the quantum phase transition from a higher-ordered excitation model to other lower-ordered one, which suggests that a nucleus populated at high-momentum state decouples firstly to the yrast-band with the E2-trasitions mode, and then to the coexist region, wherein the structure-energy is released, the change in the nucleon coupling intensity ensues, finally the basic state of the lower-ordered excitation model is reconstructed, the evolution of basic states structure is accomplished. Therefore this is a smooth and calm transition. Using an example of the 76 Sr nucleus, the problem is discussed carefully.