I remember in Fallout 3 GECK, by simply checked the repair option under AI Data tab will do the job, but New Vegas nothing has change.

How am I suppose to do to give NPC repair function?

I'm not sure how it worked in FO3, but in FNV you must have an NPC with a dialog topic, and the result script should use the command http://geck.gamesas.com/index.php/ShowRepairMenu In geck, you can use "edit->find text" and enter this name, to find out how the base game NPC's use it.

Ok then, new problem is how can I add new topic for dialog?

The GECK FAQ said right click on topic list and choose add new topic...but when I right click, there is no response.

I have learned from following the steps in the tutorials at geck.gamesas.com, and it works for me. There are also several conversation tutorials in the fallout3nexus mod talk, troubleshooting forum FAQ threads.

I found one tutorial video where by create a new quest, I can add topic in it thus I am able to add repair topic indirectly.

But is there anyway else i can add topic without going through quest creation?

The NPC where you want to add the repair menu already has some topics and some quest. The only way to do what you want is to add a topic, but you don't have to add a quest. Most NPC dialog is stored in a quest.

There is no reason NOT to add a quest. It's trivial to do so and it is a clean way to add the new dialogue to your mod. The quest form that you set up for dialogue, although it is used to organize a proper quest, can be used for only dialogue (and no quest), or can be left entirely empty except to drive a script. If you choose to set it up for dialouge, you will need to give it an ID (you don't have to name it, but you can do that as well), a priority (50 is the one the wiki suggests) and you will probably want to tick "Start Game Enabled." If you are going to be adding more dialogue in the future, and you think you will be using that dialogue repeatedly, you would also want to tick "Allow Repeated Conversation Topics." And then hit OK and your quest is created. Then you would create your dialogue there.