Chaotification is an inverse process of chaos control. This paper addresses the mechanism of chaotification of buck converter. A new chaotification model of buck converter is established. Then the chaotification rule of buck converter is discussed. The fact that using time-delay feedback at the input can realize chaotification in buck converter is proved. The ranges of control parameters are determined using nonlinear dynamics stability theory. Computer simulation is made to verify the proposed method and analyze the influence of different control parameters. The theoretical results are verified by experimental measurements.