请尝试:

mysqldump -u root -pabc Db -r "C:\Documents and Settings\All Users\Desktop\ttttt.sql"

您的命令外壳程序将路径名分成多个参数.引号告诉外壳程序将所有内容作为单个参数传递给mysqldump程序.

Your command shell is breaking apart the pathname into multiple arguments. The quotes tell the shell to pass it all as a single argument to the mysqldump program.