Cloud storage as a popular application in cloud services, are developing from single cloud service provider towards multiple cloud service providers. As a consequence, users need to manage their files from different sources and share in multi-clouds. While the conventional access control models are no longer suitable in multi-clouds environment. Therefore, a multi-clouds access control model based on XACML, named MCACM, is proposed here to implement access control in multi-clouds environment. In this model, cross-clouds access control is enabled through extending standard XACML framework. At last, we implemented a prototype of MCACM, and performance evaluation results show that our scheme is efficient.