Countersigning method and system

The invention discloses a countersigning method which comprises the following steps: 1) a document is signed by utilizing an electronic signature mode; 2) the number of the signing client sides is not less than 1; 3) the client side for initiating the countersigning is only one, and the initiating client side is responsible for submitting the signed document to the signing client side and notifying the signing client side for signature and seal; 4) all the signing client sides sign the same document, wherein the signing mode is on-line signing, and all the signing client sides are equal mutually and sign in parallel; and 5) the signed document can not be modified, and the initiating client side files the document and distributes the document to other client sides. The contact countersigning method disclosed by the invention can provide countersigning without flow restriction, and the only one source contract is locked and can not be modified in the whole countersigning process, not only is the efficiency improved, but also the uniqueness and anti-tamper property of the signed document are ensured, and the requirement of United Nations Convention on the use of Electronic Communications in International Contacts is met.