For a definite particle,the decay mode is determinant,finite kind,which embody the characteristic of quantum mechanics. But for a specific mode of a definite particle's decay,the decay spectrum,ie,energy of products,continuous,or discrete? Decay is a process which has unique initial condition,a static parent particle.So the result is very interesting. If it is continuous,why the gamma decay of nucleon has some characteristic energy? If it is discrete,the amplitude function on energy and momentum would not be continuous,so how to use the analytic way to calculate?