A synchronous rectification control circuit and method, and a flyback switched-mode power supply (SMPS) are provided. A voltage adjustment circuit is used to adjust a value of a first voltage signal that represents an output voltage, such that a voltage-second product of a difference between the output voltage and a drain-source voltage of a secondary-side synchronous rectifier can be zeroed in time in a transient process, and no false accumulation occurs. In this way, when a primary-side transistor switch is turned on, the secondary-side synchronous rectifier is turned off, to avoid a case in which the primary-side transistor switch and the secondary-side synchronous rectifier are simultaneously turned on.