Tolerance limits of different tissues to landing impact were studied by doing experiment in Rhesus monkeys. 10 Rhesus monkeys were divided into three groups, each suffered a different landing load. The monkeys were killed lh after the experiment, and heart, liver, spleen, lung, and temporal bone were fixed, sliced, and then observed under microscope. Injuries of inner-ear were also observed. The results showed that when acceleration measured at the impact platform was less than 25 G, only slight injuries were found in the various organs and no injury was found in the inner ear; when platform acceleration was 25-35 G intermediate injuries were found in the various internal organs, and slight injury was found in the inner ear, such as detachment of otolith from macula of saccule and separation of epithelium in the ampulla.