I try to install with Fetch Python Plugins. But fetch python plugins show only those which are installed? can i install manually when direct installation failed repeatedly?
Assuming you use qgis on windows7 you could unzip the plugin into: c:\user\your username.qgis\python\plugins
update: when you look here: http://fromgistors.blogspot.co.at/p/semi-automatic-classification-plugin.html you see that the plugin has some dependencies, which need to be installed first. click on the link "Information about the installation of required software" on this website to get more infos for your qgis-version (1.8 or dev/upcoming 2.0)