I was following MJ's sina weibo project video to make an app of weibo. however I can't access internet from the weibo app or safari. so google it and got the right solution which is so easy. guess what, just to restart the simulator.

http://stackoverflow.com/questions/25654679/cant-use-http-in-ios-8-simulator

solution from apple's engineer:

There is a known issue whereby changes in the host's network configuration (changing wireless networks, changing from wireless to wired, etc) will result in the simulated runtime appearing to loose network connectivity for some cases. The workaround is to just reboot the simulated device.