The solidification process of liquid metal potassium is simulated by using the molecular dynamics method. According to the evolution properties of average atomic energy in system, bonding type and clustering type among atoms, and the dynamic parameters of mean-square displacement and non-Gaussian parameter, the dynamic mechanisms in initial nucleation of supercooled liquid potassium are deeply studied. It is found that the supercooled liquid region can be divided into two different stages according to the evolutions of thermodynamic, dynamic and structural properties of supercooled liquid. And the potential crystallization nuclei appear in the lower temperature region of supercooled liquid. It is also found that the potential crystallization nuclei are formed with the disaggregations of icosahedron clusters during the -relaxation regime, and the critical size of nucleus is about 300 atoms.