  The CW RF test of 1.3 GHz 9-cell cavity in liquid helium bath at 2 K is a
very important key point in the cavity procurement. Some problems can be found
through the test, according which to optimized and improve the process of
cavity. Recently, Medium temperature (mid-T) furnace bake of 1.3 GHz 9-cell
cavities have been carried out at IHEP. Through the proceed of mid-T bake, the
quality factor of cavity has been greatly improved. While the excitation of the
parasitic modes in the high Q cavities CW cold test has been encountered, which
implies an error source for the cavity gradient and quality factor
determination. In order to ensure the testing accuracy of superconducting
cavity, we have improved the testing system. Finally, the parasitic mode is
completely suppressed and the CW RF cold test of high Q cavity is guaranteed.
