One practical and adequate approach to achieve HCCI combustion in the gasoline engine is trapping hot burned gas via fully variable valve actuation, but the control methods become complex with various adjusted valve parameters. Through the experiment research, transient response of the HCCI engine to change in the four control variables of 4VVAS were investigated respectively, and the response time for the four actuators constants were compared. It was found that, in order to realize fast transient operation in HCCI mode, appropriate coordinated and synchronous operation of the four actuators is required. The experimental results show that, during coupling regulation of the four variables, symmetric principle of valve timing and synchronal principle of valve lift are proposed to simplify coupling strategy and improve IMEP transition. The obtained result forms the foundation of transient control strategy for the HCCI engine based on the 4VVAS.