China's National Bureau of Statistics said that the annual growth of housing price reached 24% in 2009 after the financial tsunami. Is it a recovery or a bubble? What makes the housing price increasing so quickly? Price-to-Income Ratio is by far the commonest measurement method to housing affordability. And the relatively high housing price-to-income ratio in Asian cities, especially in Mainland China has been aroused many researchers' attention. In this research, the writer use panel regression based on monthly data from 2005 to 2009 of Mainland China cities, to analyze the driving factors of housing price-to-income ratio and also housing price and household income separately. And the test results suggest that the housing price boom might lead to a bubble.