Multi-resonant switched capacitor converter can make efficient use of active and passive components， and has two characteristics of high efficiency and highly power density. Therefore， we propose a 9：1 cascaded multi-resonant switched capacitor converter and further explore ways to improve the performance of the converter in this paper. On the one hand， by analyzing the coupling relationship between the first and second circuit topology， we propose a method to reduce the intermediate decoupling capacitance. On the other hand， by adjusting the dead time of the control signal， the zero-voltage switch (ZVS) of most switching devices is realized， and the efficiency of the converter is improved. Therefore， a 48 V-5 V resonant converter prototype with rated power of 120W，power density of 330 W/in3，peak efficiency of 98.1% and maximum output current of 23.7 A is designed in this paper. From 20% to full load， the efficiency is al-ways maintained at more than 92% (including driving loss)， and most of the loss is reflected in the conduction path， reflecting great optimal space and application potential.