The housing-price-to-income ratio is a widely accepted indicator for housing purchasing power analysis in western countries, and there are some researchers who study the housing purchasing power with it in China. However, systematic studies about this problem are not rich. In this paper, the indicator is reviewed first and models are proposed to analyze the affordable housing-price-to-income ratio based on the expenditure structure matrix of households. What＇ s more, the affordable house prices of different income classes are derived. As a demonstration, housing purchasing power of Beijing in 2004 is analyzed from these two aspects. In the demonstration, the affordable housing price and the affordable-price-to-income ratio of each income class are computed based on the family cost matrix. The results show that lower-middle income class cannot afford forward delivery housing, and some corresponding suggestions are proposed in the conclusion