A 2998MHz, 60MW klystron has been developed for future linear accelerators of synchrotron radiation sources. In order to save development and construction time, the 2998MHz, 60MW klystron is a modified version of an existing 2856MHz klystron used in linear accelerator of Beijing Electron-Positron Collider II. Based on the simulations, it was shown that the scaled version klystron was able to produce more than 60MW at a 350kV beam voltage. A prototype was built and tested. It successfully produced 50MW output power with an RF pulse width of 4.0ms, which exceeded the operating requirement of China's High Energy Photon Source. It also produced 62MW with an RF pulse width of 1.6ms, which proved the validity of new RF circuit design. This paper describes the details of the progresses of this klystron and advantages of this tube development.