The invention provides a triangular wave generating circuit and a method thereof. The triangular wave generating circuit comprises an integral circuit, a level detecting circuit and a signal adjusting circuit, wherein the integral circuit generates a triangular wave output signal according to the state of integral current; the level detecting circuit receives the triangular wave output signal, when the level of the triangular wave output signal is up to the first reference level, and the detecting signal is outputted; the signal adjusting circuit ensures that the integral current is in the first state according to the detecting signal to change the level of the voltage of the triangular wave output signal and to generate the edge pulse signal according to one clock; moreover, according tothe edge pulse signal, the level of the voltage of the triangular wave output signal is extended to the second reference level; according to the edge pulse signal, the integral current is in the second state so as to change the level of the voltage of the triangular wave output signal.