Nowadays the public's familiarity with classical momentum is almost as good as energy. The law of conservation of momentum is deeply rooted in the hearts of the people. The center collision effect of equal-mass balls is even used in entertainment programs and dances. This article demonstrates the application of quantum momentum by estimating several typical physical examples in quantum theory, leading readers to reveal the nature of momentum step by step, and also enable readers to deeply understand the physics of wave functions in quantum mechanics.