With the rising rate of aging, aging at home has become an important issue to Taiwan government. And, the public housing, as a policy, is a method that government can
improve the living environment quality and make the housing market developing in normal.Through the policy, not only can the government solve the house-buying problem of low and middle-income earners, but also control the quality of the urban living environment. In comparison to other housing communities, public has more elderly and lower building coverage rate, therefore, facing to elderly renovation public housing is more imperious and has more advantage. Reviewing advanced elderly-related study, there is no study for making decision and treating difficulties of elderly renovation. According on the above-mentioned, a study on renovation assessment is needed. Therefore, The study uses MCDM(Multiple Criteria Decision Making) to establish an assessment system of exiting public housing by references and AHP. Finally, three public housing communities are selected to apply the assessment system. About the difficulties of renovation, the study choose a real case to establish a renovation model. The study uses the model to discuss the difficulties of skills application, renovation subsidies and law limits. The conclusion is as follows：
1. The renovation assessment system of exiting public housing：Establish the assessment system by previous works, expert interviews and AHP.
2. The weighting of each renovation item：
The outcome shows that interior environment is the most important item in environmentlevel; moving function of interior environment is the most important item in function level;floor barrier is the most important item in assessment item level.
3. The prior renovation items for deferent decision maker：
According to deferent decision maker in each environment, suggest them the priorrenovation items.
4. The analyze of real case：
With the construction time was getting close, the consideration for elderly had improved
in housing environment, community environment and urban environment. There was no improvement in interior environment during the past 20 years.
5. The discussion of renovation difficulties：
(1)Skills aspect：Reduce the difficulties of renovation by prompting wireless tech.
(2)Economic aspect：For interior environment, government should subsidize the prior renovation items; for housing environment, government should subsidize high-cost item,
such as: elevator; for community environment, government can subsidize the community activities.
(3)Law aspect：Suggest government open up the limits of building bulk control.