The trust decision-making is very important to people in Electronic Commerce transactions. The approaches that assist people to finish trust decision-making become a basic issue that researcher must face and solve imminently in the field. A new quantificational subjective trust evaluation approach based on the cloud model is presented. The expected value and hyper entropy of subjective cloud is used to evaluate the reputation of trust objects, and a trust change cloud model is designed to depict the reputation change style of trust objects in order to provide additional evidence. The result of simulating experiments shows the validity and effectiveness of this approach.