Under sedentary fatigue, the unconscious unhealthy posture of people leads to the gradual rejuvenation of chronic diseases such as cervical vertebrae and lumbar vertebrae. In the case of long office hours, it is key to help young people maintain a healthy sitting posture and reduce the load of sedentary activities on their bodies. Using the KJ method, through processes such as observing the sitting postures of the target group, conducting user interviews, creating user journey maps, combining demand screening, and analyzing the postural changes and adjustment behaviors of the target group in office settings, 13 key design requirements were identified. Based on this, a hierarchical analysis of user demands was carried out by KANO model. Then, a FBM model was used to transform the expected attribute and charm attribute into the target behavior for cost screening. Ultimately, the low-cost and low-ability behavior was retained, the behavior-oriented improvement design of office furniture was carried out around the multi-posture alternating office. In conclusion, through the application of the KJ method -KANO model -FBM model, the demand level of sedentary young people for office furniture is clarified. Introducing the posture of kneeling, squatting and sitting cross-legged into office behavior provides a new solution and research idea for relieving the pressure of sedentary on the body.