Brain　structure　and　cognitive　function　change　in　the　temporal　lobe,　hippocampus,　and　prefrontal　cortex　of　patients　with　mild　cognitive　impairment　and　Alzheimer＇s　disease,　and　brain　network-connection　strength,　network　efficiency,　and　nodal　attributes　are　abnormal.　However,　existing　research　has　only　analyzed　the　differences　between　these　patients　and　normal　controls.　In　this　study,　we　constructed　brain　networks　using　resting-state　functional　MRI　data　that　was　extracted　from　four　populations　(normal　controls,　patients　with　early　mild　cognitive　impairment,　patients　with　late　mild　cognitive　impairment,　and　patients　with　Alzheimer＇s　disease)　using　the　Alzheimer＇s　Disease　Neuroimaging　Initiative　data　set.　The　aim　was　to　analyze　the　characteristics　of　resting-state　functional　neural　networks,　and　to　observe　mild　cognitive　impairment　at　different　stages　before　the　transformation　to　Alzheimer＇s　disease.　Results　showed　that　as　cognitive　deficits　increased　across　the　four　groups,　the　shortest　path　in　the　resting-state　functional　network　gradually　increased,　while　clustering　coefficients　gradually　decreased.　This　evidence　indicates　that　dementia　is　associated　with　a　decline　of　brain　network　efficiency.　In　addition,　the　changes　in　functional　networks　revealed　the　progressive　deterioration　of　network　function　across　brain　regions　from　healthy　elderly　adults　to　those　with　mild　cognitive　impairment　and　Alzheimer＇s　disease.　The　alterations　of　node　attributes　in　brain　regions　may　reflect　the　cognitive　functions　in　brain　regions,　and　we　speculate　that　early　impairments　in　memory,　hearing,　and　language　function　can　eventually　lead　to　diffuse　brain　injury　and　other　cognitive　impairments.