Dinesh,
SMQ1 is not a log. It is a listing of Queues that have not processed.
In general, it is not wise to delete any entries from SMQ1 unless you first investigate; particularly in a productive system. In many cases, these entries represent interface failures; e.g. a bit of data that was SUPPOSED to update a destination system in fact did not perform the update. In such cases, the systems may be out of synch, and that inconsistency might represent genuine business problems.
The other experts have described how to perform the deletions, once you have decided that the entries should be deleted. However, I strongly recommend that you at least look at samples of each failure, and first determine if deletion is the only step that must be performed. Depending upon the contents of the queue, there may be other steps you should take as well.....
Best Regards,
DB49