Abstract: To study the changes of central cholinergic system on high altitude hypoxia and the mechanism of the toxicity increasing of organophosphate compounds at high altitute.The activity of AChE and the concentration of ACh were meaused by spectrophotometric method,the binding of M receptor was detected with the antigonist and protein content was assayed by Folin phenol method.Under the condition of simulated 4000 m altitude,the activity of AChE increased in different extent,the density and affinity of M receptor raised significantly at 24 and 72h,but the ACh decreased;the density of striatum during soman intoxication at simulated high altitude enhanced remarkably compared with single soman intoxication group.It shows that the cholinergic system of Striatum was sensitive on high altitude hypoxia and soman intoxication,the up regulation of cholinergic system plays most important roles in the toxicity increasing of organophosphate compounds at high altitude.