I just find youtobe is forbidden in China several days ago. Today my classmate told me one tool can solve this problem
download UltraVPN : https://www.ultravpn.fr/download/ultravpn-install.exe
install it and register a free account in https://www.ultravpn.fr/account.htm
then use this account to signin. After the small icon in your right bottom area of PC turns to green, you can visit www.youtobe.com again. Good Luck.