Providing a provable and verifiable execution environment for the tenants is a very important problem in the cloud computing mode. This paper proposes a dynamic trustworthiness verification mechanism for the tenants' virtual execution environment, named TCEE (trusted cloud execution environment), which extends the current trusted chain into virtual machine's architecture stack. It cyclically verifies the trustworthiness of the memory and file systems within the virtual execution environments. TCEE introduces a TTP (trusted third party) to perform the verification and audit action against tenants' virtual machines to avoid heavy involvement of end tenants and unnecessary information leakage of the cloud providers. A prove-of-concept prototype is implemented according to TCEE to evaluate the effectiveness and the performance overhead incurred. Experimental results show that TCEE is effective and its performance overhead is minor.