Constant current controlled primary-side regulation (PSR) flyback converter is widely used for its small volume, low cost and simple control. As the output current could not be sensed and controlled directly, the secondary-side output diode current is kept unchanged to ensure that the output current remains constant. However, the dynamic performance of the converter would inevitably deteriorate as the output current returns to the target value exponentially. To improve the dynamic response, an improved dynamic control method is proposed in this article. Based on the exponential attenuation characteristic of the output voltage during dynamic transition, the load is monitored and estimated. The dynamic performance is improved with two dynamic modes and elimination of potential output resonance. The proposed digital control method is verified through a field programmable gate array controlled 5-V/1-A PSR flyback converter with discontinuous conduction modulation mode. Compared with traditional PSR control method, the dynamic performance is improved. The response time is reduced from 5.30 ms to 1.44 ms when load changes from 5 Ω to 3 Ω, and from 7.00 ms to 1.58 ms when load changes from 3 Ω to 5 Ω, respectively.