An input method, device and system applied to a mobile smart terminal. The method includes: establishing communication connection with a virtual reality device; collecting input information of a user on the mobile smart terminal; and generating a corresponding operating instruction according to the input information and a corresponding matching relationship between preset instruction and input information in a preset instruction database, and sending the generated operating instruction to the virtual reality device, to enable the virtual reality device to execute a corresponding operation according to the operating instruction. An input device and an input system corresponding to the method are also provided. According to the input method, device and system, a corresponding operating instruction is generated by using the user input signal received on the mobile smart terminal to control the virtual reality device, thereby avoiding purchasing a gamepad, saving users money, facilitating the use, and improving the user experience.