>Recently , I find that there is timeout occur when runing 'select .
>statement'
>Some said the Transaction Log too large will make SQL become slowly
>
>Now, the transaction log is 14407M , is it too large ? Can I delete it ? (Do
>I need to do backup first ?)


Is it too big? Yes.
See "Truncating the Transaction Log" in SQL Server Books Online (BOL)