In this paper we examine the applicability of some indexes such as housing-price-to-rental ratio,vacancy rate that always used by academic circle to measure the bubble of housing market.We demonstrate that these indexes are all unsuitable to be the direct and accurate index to measure the bubble level of China's urban housing market because of the objective conditions of the country,and that the most suitable index for measuring the bubble level of housing market under the current condition is the housing-price-to-income ratio.We construct a model to measure the reasonable limit of hosing-price-to-income ratio,then based on China's current mortgage loan's rate level and period and down payment ratio,deriving that the country's urban resident's sustainable housing-price-to-income ratio limit is no more than 7.Then using statistics data,we figure out current hosing-price-to-income ratio of our country's major cities,and draw the conclusion that in recent years the country's urban housing market exists bubble overall,especially at present urban housing market bubble is very significant.Part of the First-tier city's bubble is so amazing and contains huge financial risk.Based on above analysis,we put forward some policy suggestions.