Cloud Computing has been envisioned as the next-generation architecture of IT Enterprise. More and more users store data in "clouds". As such, it has become crucial for an archive service to be capable of providing evidence to demonstrate the integrity of data for which it is responsible. This work studies the problem of ensuring the integrity of data storage in Cloud Computing. In our work, we consider the task of allowing a third party verifier (TPV), on behalf of the cloud client, to verify the integrity of the dynamic data stored in the cloud. In particular, to achieve efficient data dynamics, we improve the Proof of Retrievability model by manipulating the classic Merkle Hash Tree (MHT) construction for block tag authentication. Extensive performance analysis show that the proposed scheme is highly efficient.