The invention discloses a trust negotiation protocol designing method under a complex cloud environment. The method comprises the following steps: a request side recommends an information request to all providers for initiating the service to one or more user sides associated with the request side; the request side acquires recommendation information of one or more user sides within the predefined time so as to generate a provider list; the current trust value of each provider is queried according to the provider list; the provider with the highest trust value is determined as the provider of the service, and a negotiation request is initiated to the service provider; the service provider confirms the current trust value of the request side, and starts the negotiation with the request side if the current trust value of the request side belongs to the trust range; and the service provider launches the service after the negotiation.