The competition in the land market is drasticly increasing, which demands much higher scientificity and accuracy in the decision. The land investment decision system is a non-linear gray system and the traditional appraisal methods have some limit in appraising it. It uses cloud model and the uncertain illation based on the cloud model, translates the qualitative appraisal of the factors level into quantitative scores, achieves the transition between a linguistic term of a qualitative concept and its numerical representation ; and further merges the degree of gray relationship theory to appraise the comprehensive level of the objects. So the new decision mode is set up. Through an example analysis and contrast study, the validity of the method is validated. The application of cloud theory in the decision field will affirmatively improve the decision level.