PaaSs emerge to help SaaS providers to conquer the challenges involved in guaranteeing the QoS of international SaaSs. A well structured machine readable SLA is critical for PaaS providers to automate InterCloud management to serve the worldwide elastic user demands. WS-Agreement is a widely accepted extendible language for describing agreements. In this paper, we propose PSLA, a well structured PaaS Level SLA description language based on WS-Agreement. We summarize and describe the semantic clauses needed to be considered in PaaS level SLA. In particular, some specific characteristics of PaaS are taken into account in PSLA, such as elasticity of workload, undefined metric properties and fuzzy value range.