The goal of this study is to study the feature of posture homeostasis in prolonged sitting of normals, in order to provide information to electrical wheelchair designer to design ideal wheelchair to help people who cannot functionally reposition themselves and relief pressures under their bony prominences. Subjects sat on a powered wheelchair which seat inclination can be adjusted. We used a pressure mat to measure the pressure under hip and back during prolonged wheelchair sitting, then calculated the center of pressure (COP) to analyzed the mode and range of posture change in different seat inclination. The study included 10 healthy subjects. The results showed that in these 10 subjects, the COP movement of 100°, 110°, 120° and 130° in the sagittal plane was 11.5±6.5, 11.1±4.3, 11.4±5.8, and 12.8±5.5cm, and in the coronal plane was 7.1±5.4, 4.2±5.5, 4.7±6.9, and 5.0±5.1.Through one-way ANOVA, we found statistically significant differences (p-value < 0.05). When separated different sex in two group, we found that male motion extent in sagittal and coronal plane were 11.7 ± 0.7 and 6.5 ± 1.8, and female were 10.2 ± 1.9 and 3.9 ± 1.6. There was significant difference between motion extent of males and females. Males moved to a larger extent than females (p < 0.05). In addition, the same subjects seated in the experimental design in four different angles, two to four will show similar features. The features of posture homeostasis in sitting of different subjects somehow may have significant differences.