The present invention provides a method for writing motion recognition, wherein a sound signal generated when a writing apparatus is contacting and moving on a writing surface is acquired. According to the occurrence of the sound signal, the writing apparatus can be determined whether it is on the writing surface or not. In another embodiment, the present invention further provides a method for writing trajectory recognition, wherein the foregoing method and character recognition techniques are combined to convert a writing trajectory into a character. In addition, the present invention further provides a writing apparatus and a recognition system, wherein a device is installed in the writing apparatus for collecting sound signal generated during the writing process and a processing unit which adapts the foregoing method is used to recognize the motion trajectory of the writing apparatus so as to form the corresponding character.