"合约式联营企业" can be translated into English as "contractual joint venture enterprise" or simply "contractual joint venture".
This term refers to a business arrangement where two or more parties come together through a contractual agreement to form a joint venture for a specific purpose or project, without necessarily creating a new legal entity (though in some cases, a separate legal entity may be established depending on the jurisdiction and the specifics of the agreement).
In legal and business contexts, "contractual joint venture" is a commonly used and recognized term.