Microwave vacuum electronic devices play a crucial role in various fields such as scientific research and industry. Particularly, the klystron has been essential in nuclear fusion research, high-energy physics experiments, and industrial radiation processing. The output coupler, a key component of the klystron, directly impacts its overall performance. However, coupler failures are among the most common issues in klystrons and various vacuum electronic devices, especially prominent in scenarios involving high continuous wave power operation. For the development of a high-efficiency tunable 650 MHz/800 kW continuous wave klystron, optimization design of the output coupler was conducted. Significant progress was achieved in the testing of the output couplers for single-beam and multi-beam tunable klystrons. In continuous wave mode, the test power of the output coupler for the single-beam tunable klystron has exceeded 690 kW. To further increase power capacity, a T-bar transition structure was employed, and the coupler was optimized to achieve a more uniform electric field distribution near the ceramic. Additionally, the rectangular waveguide window output coupler for the multi-beam tunable klystron achieved a maximum test power of 115 kW in full standing wave conditions.