Effective removal of mudcake from the wellbore before cementing is critical to developing an excellent bond between cement and formation. The application of spacer can remove mudcake effectively. The evaluation of mudcake removal efficiency is significant to the design of spacer. The methods proposed by scholars have limits on the development of mudcake and the simulation of the flushing process. For this paper, a novel apparatus used to test mudcake removal efficiency was designed. A novel experimental method for mudcake removal efficiency of spacer was proposed. The influence factors of mudcake removal efficiency are discussed. The method can evaluate the flushing efficiency quantitatively and provide guidance for designing of spacer.