Abstract: There exists risk caused by incomplete cost information of CSP (cloud service provider) when customer enterprise is carrying out SaaS(Software as a service) cloud outsourcing. Focused on the incomplete information problem caused by the unobserved efficiency parameter in cost structure of CSP, although the service quality is verifiable, the contract is designed to induce CSP show the real cost structure information and provide the optimal service quality, effort, and the contract incentive effect is finally compared with complete information. The conclusions imply that the incentive compatibility constraint of CSP with higher efficiency parameter and the participation constraint of CSP with lower efficiency parameter can be ignored when the outsourcing contract is designed; the marginal cost of CSP with higher efficiency parameter is not lower than the CSP with lower efficiency parameter, otherwise, the service quality performs to the opposite; the optimal service quality and effort of CSP with higher efficiency parameter under incomplete information is not higher than the service quality and effort under complete information, the service payment performs to the same; the optimal service quality and effort of CSP with lower efficiency parameter under incomplete information are the same as the service quality and effort under complete information, and the service payment under incomplete information is not lower than the service payment under complete information.

Key words: cloud service provider (CSP), efficiency parameter, service quality, incomplete information, contract design