After work with 3.x scripts manual, I can not search key word, how can I fix this problem.
Considering that Unity 3 is currently a beta, I would recommend patience, and hope they fix it in the next build.
There is nothing you can do on your own unless you go into the file (Unity saves a copy of the manual to your computer) and add a searching algorithm which would really be a waste of time considering Unity will add the functionality themselves in the near future unless you REALLY need a search bar. I don't know why you would considering you can find all of the classes in a list if you need a new 3.0 class or use the search in the previous version which gives you all the old methods and classes which is still the majority of the Unity API. So unless you are searching for a lightmapping scripting term, you might be better off searching it in the old reference.