A stylus is provided. The stylus comprises a main body and a functional part. The main body includes a first processor, a trigger coupled to the first processor, and a connection interface coupled to the first processor. The functional part includes a functional module. The functional module is detachably coupled to the connection interface. When the functional part is coupled to the connection interface, the first processor determines a function of the functional module via the connection interface. The first processor enables the functional module when the trigger is triggered. An operating method for a stylus is also provided.