The present disclosure introduces a method, a system and an apparatus of implementing online transaction according to Open API. In one aspect, a method includes: receiving a first invocation request to invoke an Open API from a third party development server according to a user's transaction request; determining an ISP server corresponding to the Open API as requested to be invoked in the invocation request; sending the first invocation request to the determined ISP server; receiving a service page returned by the ISP server according to the first invocation request; and sending the service page to the third party development server for processing the service page and sending the processed service page to the user, the processing comprising embedding the service page into a page corresponding to the transaction request.