A method for a communication device to automatic respond to an incoming call is provided. The method includes: configuring a destination and a message template; detecting whether there is an obstruction in front of the communication device and a picture taken by a rear camera is in an even color when an incoming call is received; turning off a ringtone of the incoming call if there is an obstruction and the picture is in an even color; detecting a current position and position variation by a GPS unit; calculating an average speed based on the position variation; and hanging up the incoming call, calculating a time required to reach the destination, filling out the message template with the time required to form a predefined message, and then transmitting the predefined message to the caller of the incoming call if the average speed equals to or exceed a predefined value.
