In this study due to the increasing amount of quality problems that arise in organizations, some of these problems in Tehran municipality are being tested. First, a large number of projects that need to be improved are defined by one of multiple decision-making method of MCDM named ANP priorities. Then, the most important projects have been selected. For doing this project, some problems arise that parts of their information are known and some are unknown. To identify and select the problems, gray systems are being used, and the main problem can be found by using "gray possible degree" that are the new decision-making techniques and evaluate mathematical data which are vague and uncertain. The identified problem is analysis by using the methodology of Six Sigma and DMAIC cycle. By using Pareto charts and Minitab software the main causes of the issues have been identified and resolved. Finally, by using creative and innovative techniques, the problem solving capability of TRIZ is improved.