Through observing the changes of ultra-structure of cerebral cortex in rats after different exercise load swim training,the result shows that the ultra-structure in rats' cerebral cortex was changed after overtraining.The moderate-exercise training can increase the quantity of cerebral cortex micro vessels and mitochondrion.The change of ultra-structure in cerebral cortex microcirculation can induce the dysfunction of cholinergic neuron and further cause the exercise-induced central fatigue.