Objective To evaluate the characteristics of spatial distribution and time accumulation of impact acceleration at different parts of human body during backward falling process. Methods Four healthy men and four healthy women (20-20 years old) were enrolled. The tri-axial acceleration on head, chest, left/right arm/hand/foot, left/right front/back hip, left/right femur head, sacrum and coccyx throughout the backward falling were measured by ADXL335 tri-axial acceleration sensor. Systemic acceleration distribution of backward falling was polynomial fitted by signal magnitude vector (SMV) of its first peak. Besides, parameters of impulse mechanics such as zero-g time, total falling time, peak SMV, relative pressure impulse of the vulnerable sites (head, hip and its related sites) were also calculated. Results Compared with the other parts of the body, the peak SMV and relative impulses of left/right back hip and head were significantly higher (P＜0.05). Acceleration that paralleled to the ground in left/right back hip was also relatively large. The rotational transform angles of left/right back hip, left/right femur head, sacrum and coccyx were significantly larger (P＜0.05). In addition, during the process of falling backward to the ground, a sliding tendency toward the sagittal plane 53.58°±6.75° occurred at all testing sites. Conclusions Head and hips are vulnerable during backward falling, and their zero-g time (0.26±0.05) s can be used as the longest starting time of falling protection devices. The large change angle of left/right hip, left/right femoral head, sacrum and coccyx may be the important cause of the sprain during backward falling.