Download and install Git from MSysGit or Git SCM.
Download and install getopt.exe from the util-linux package into C:\Program Files\Git\bin. (Only getopt.exe, the others util-linux files are not used). Also install libintl3.dll and libiconv2.dll from the Dependencies packages (libintl and libiconv), into the same directory.
Suppose that Git is installed in the folder
c:\bin\gitand GnuWin32 in the folderc:\bin\GnuWin32.
Clone the git-flow sources from GitHub:
$ git clone --recursive git://github.com/nvie/gitflow.git
Run the msysgit-install script from a command-line prompt (you may have to
run it with "Full Administrator" rights if you installed msysgit with its
installer, and ensure you're running from a Windows command prompt, not MINGW):
cd gitflow
cp c:\bin\GnuWin32\bin\getopt.exe c:\bin\git\bin\getopt.exe
cp c:\bin\GnuWin32\bin\libintl3.dll c:\bin\git\bin\libintl3.dll
cp c:\bin\GnuWin32\bin\libiconv2.dll c:\bin\git\bin\libiconv2.dll
contrib\msysgit-install.cmd c:\bin\git
In Git bash create a symbolic link for git-flow so that you can actually use the $ git flow command from any location.
ln -s /C/gitflow/git-flow git-flow
The most easy way to install git-flow on Windows (if you already have NPM)
https://www.npmjs.com/package/git-flow
npm i -g git-flowEnd.