In the Infrastructure as a Service (IaaS) industry, the decision-making to choose the prioritized trust improvement actions is significant as to ensure the trustworthiness and service continuity of the IaaS cloud providers. This is done by checking the trust control elements (TCEs) of IaaS cloud regularly so as to put together an efficient and effective improvement plan. However, it is very difficult to put such improvement plan unless it is based on the results of a preparatory evaluation. This paper, present rigorous and reliable evaluation framework based evaluation theory called trust evaluation of IaaS cloud framework. The main goal of this evaluation framework is to help IaaS cloud providers to identify the unimproved gaps according to particular TCEs. Diagrammatic trust tree and hybrid evaluation and ranking technique combining fuzzy set, simple additive weight, and important performance analysis (IPA) are the main components of this novel framework. The proposed framework is applied to evaluate the IaaS cloud of two providers. The results show that each provider has several different unimproved gaps that need urgent improvement actions. Moreover, based on the analysis results of IPA, several recommendations have been suggested to fill these gaps. © 2015, Springer Science+Business Media New York.