比你想象的要复杂得多！请参阅此处：使用C＃备份SQL数据库 [ ^ ]

Slightly more complex than you think! See here: Backing up an SQL Database in C#[^]

尝试在数据库名称周围加上方括号：

Try to put square brackets around the database name:

BACKUP DATABASE [Ast-db] TO DISK

 string path="D:/filename.bak";
SqlCommand cmd=new SqlCommand("backup database dbnameto disk='"+path+"'",con);
 int a=cmd.ExecuteNonQuery();