A one cycle control method for power factor correction, which is implemented by software integrated into a main control chip in cooperation with a boost circuit, the boost circuit comprising an AC input, a rectifying circuit, an inductor, fast recovery diodes, a capacitor, a DC output, an inductive current sampling circuit, an output voltage sampling circuit, a switch transistor and a driving circuit of the switch transistor; characterized in that the control method comprises the steps of: Determining whether soft-start ends or not; if the soft-start ends, processing step directly, if not, increasing reference value U ref of output voltage and then processing step; Reading sampling output voltage U o and sampling inductive current i g according to A/D sampling triggering instant; Calculating as follows duty ratio of PWM signal for driving the switch transistor: Calculating u 1 and u 2 according to Equation of { u 1 t = i g nT R s u m nT u 2 t = 1 T ∫ 0 t 1 dτ 0 ≤ t ≤ T 0 ≤ τ ≤ t in which R s is an equivalent current detection resistance, u m is an output of a PI regulator by regulating difference between the reference value U ref of the output voltage and the sampling output voltage U o; obtaining the duty ratio of PWM signal; Outputting PWM signal; Determining turn-on time of the switch transistor according to the duty ratio of PWM signal for driving the switch transistor; if the turn-on time of the switch transistor is longer than that of the turn-off time, a sampling triggering instant being selected between 50 percent and 80 percent of the turn-on time; or else, the sampling triggering instant being selected between 50 percent and 80 percent of the turn-off time; Returning to step. Determining whether soft-start ends or not; if the soft-start ends, processing step directly, if not, increasing reference value U ref of output voltage and then processing step; Reading sampling output voltage U o and sampling inductive current i g according to A/D sampling triggering instant; Calculating as follows duty ratio of PWM signal for driving the switch transistor: Calculating u 1 and u 2 according to Equation of { u 1 t = i g nT R s u m nT u 2 t = 1 T ∫ 0 t 1 dτ 0 ≤ t ≤ T 0 ≤ τ ≤ t in which R s is an equivalent current detection resistance, u m is an output of a PI regulator by regulating difference between the reference value U ref of the output voltage and the sampling output voltage U o; obtaining the duty ratio of PWM signal; Calculating u 1 and u 2 according to Equation of { u 1 t = i g nT R s u m nT u 2 t = 1 T ∫ 0 t 1 dτ 0 ≤ t ≤ T 0 ≤ τ ≤ t in which R s is an equivalent current detection resistance, u m is an output of a PI regulator by regulating difference between the reference value U ref of the output voltage and the sampling output voltage U o; obtaining the duty ratio of PWM signal; Outputting PWM signal; Determining turn-on time of the switch transistor according to the duty ratio of PWM signal for driving the switch transistor; if the turn-on time of the switch transistor is longer than that of the turn-off time, a sampling triggering instant being selected between 50 percent and 80 percent of the turn-on time; or else, the sampling triggering instant being selected between 50 percent and 80 percent of the turn-off time; Returning to step.