I build a simple application based on arduino,using bluetooth in smartphone to connect to the arduino's bluetooth module. But arduino did'nt respond.I find that the app in the phone send a hex every time.And i think Serial.read() read a character every time,not a hex.Does it matters when i using this app to communicate wite the bluetooth module ?
A character sent is still just a character sent. It all depends on how that character is interpreted. An "A" sent from one device can be read as an "A" or decimal 65 or hexadecimal 41. Even in octal or binary.
The problem you're most likely having is what a lot of us are having an issue with. Some of us believe that the bluetooth protocol implemented in some android devices isn't complete (that's my opinion anyway).
Please see: http://arduino.cc/forum/index.php/topic,105045.0.html and http://arduino.cc/forum/index.php/topic,120113.0.html for some help.
Good luck