Cassegrain antennas, as crucial optical antennas, find widespread application in space laser communication. With the increasing demands of communication, there is a continuous rise in the requirements for antenna transmission efficiency. However, the unavoidable secondary mirror obstruction issue significantly hampers transmission efficiency and complicates communication. In order to address this problem and eliminate the adverse effects of secondary mirror obstruction, this paper proposes a novel method to enhance Cassegrain antenna transmission efficiency based on multi-plane light converter (MPLC) technology. MPLC is utilized to transform communication Gaussian beams into hollow Gaussian beams that matches the Cassegrain antenna's obscuration ratio, ensuring that the outgoing beam fills the effective range of the Cassegrain antenna while avoiding secondary mirror obstruction. This method is applicable to Cassegrain antennas with varying obscuration ratios and can substantially improve transmission efficiency, reducing communication complexity. It holds significance for research in long-distance space laser communication.