In order to make the elderly enjoy the convenience brought by the more developed 5G communication network at the same time, this paper proposes an interactive mode that conforms to the physiological and cognitive characteristics of the user group and can communicate with others naturally. Based on the thinking logic of handwriting input, the interactive logic of deductive and inferential operates and the terminal product of information input is designed by this method. Firstly, according to the user's cognitive experience, this paper analyzes the logical deduction between the perception information mode and the operation task flow of the sensing device by the situational awareness technology and the algorithm of neural network; Secondly, this paper analyzes the interaction logic of the CDL-DFCM of stroke input to explore the intention of user's information input; Finally, the human-computer interaction prototype is design of the corresponding product according to the above analysis. Through a design case, the feasibility is verified, that user behavior logic deduces the operation logic method of interaction prototype. To improve the user experience of the interaction model, an interactive input terminal suitable for elderly users is designed by deductive analysis.