This article proposes a current mode control BUCK structure with a fast response and high efficiency by designing a high-speed output detection circuit. When switching between loads，the system loop quickly responds，and the transient bias current rapidly increases，resulting in a smaller transient voltage. The proposed instantaneous gain enhancement path structure is implemented with a TSMC 180-nm process. Simulation results show that in typical applications，when the load current switches between 1 and 1. 5 A，the transient output voltage is within 26 mV. The transient voltages of traditional structures with and without feedforward capacitors are 46 and 74 mV，respectively； thus，the proposed system reduces these by approximately 43% and 65%，respectively，and significantly improves transient response speeds. Additionally，the peak efficiency can reach 96%.