Cmake error when creating a new workspace in windows

edit

when i creating a new workspace(in windouws) using

colcon build --merge-install

this error happend.

CMake Error at CMakeLists.txt:31 (findcolcon package):
  By not providing "FindQt5.cmake" in CMAKE_MODULE_PATH this project has
  asked CMake to find a package configuration file provided by "Qt5", but
  CMake did not find one.
Could not find a package configuration file provided by "Qt5" (requested
  version 5.9.5) with any of the following names:

    Qt5Config.cmake
    qt5-config.cmake

  Add the installation prefix of "Qt5" to CMAKE_PREFIX_PATH or set "Qt5_DIR"
  to a directory containing one of the above files.  If "Qt5" provides a
  separate development package or SDK, be sure it has been installed.

i dont know why,and dont konw how to fix it. Does someone konw how to fix it? Iwould be appreciated!