And I want to know is drupal 7 ready for a product site now? I saw there is a lot of modules are beta , even the most popular module Views is beta and has some bug I meet.
Yes, most drupal 7 modules are still in beta phase. Its better you use Drupal 6 if you are going to use any beta Drupal 7 module.
We've started recently to use D7 base but if you dont have must custom module experience then D6 is probably better if you need the job done now. The best answer though is to try see what modules you'll need. The big ones like Views, panels etc are fine in D7.
I would recommend you to use drupal 6 since drupal 7 doesn't have much modules and themes as compared to drupal 6. Also as you mentioned most of the drupal 7 modules are in beta phase.
Drupal 7 will probably be fine but you need to have a thorough audit of the third-party modules you are going to need and whether they are ready for Drupal 7 yet.