A ratio buck-boost (RBB) converter with feed-forward (FF) technique is proposed for regulating output voltage with fast line response. Owing to the ratio control technique, RBB converter can achieve high conversion efficiency due to only two turn-on switches within a switching period for all operation modes, which contains buck, boost, and buck-boost modes. Besides, feed-forward technique minimizes the voltage variations at the output of error amplifier. Thus, a fast line transient response can be achieved with small dropout voltage at the output. The proposed RBB converter with FF-technique is designed by TSMC 0.35um 2P4M process. Simulation results demonstrate the correction and performance of RBB converter with FF-technique. The transient dropout voltage can be decreased from 80mV to 3mV.