I go to All Settings make shopallthemepluginintegrationsettings.integratenopajaxcart > True, Nop Ajax Cart can work, but Nop Shop All Theme > settings still not see Integration of Nop Ajax Cart.
and in this way, Nop Ajax Cart will brought error of different good. the meaning that buy no.1 will give me no.2.
What version of nopCommerce are you using?
The Ajax Cart plugin now is integrated by widget, so there is no need for the setting that you are trying to add.
Please update you theme and plugins (you can do this by reading the following article http://www.nop-templates.com/t/How-To-Update-A-NopCommerce-Theme
After that go to the Settings of your Ajax Cart plugin and make sure that the Enable Nop Ajax Cart
setting is checked.