Can I buy sim card here in hongkong to china mobile store ..

Khate, I don't think it's a good idea for you to buy China Mobile sim card when you are in HK. Your destination is southern mainland China. You can buy a sim card when you arrive at your destination city. The cost should be a little cheaper. You should buy the sim card according to your mobile phone mode. If it supports GSM only, then you need to buy a sim card from China Mobile. If it supports WCDMA only, then you need to buy one from China Unicom. If it supports CDMA only, you should buy one from China Telecom.