The high-speed development demands new real estate investment theory. Using the experiences of the Western developed countries for reference in property investment and modern portfolio investment theory, the paper introduces the conception of systematic and unsystematic risk with the centre of risk and profit. Consequently, the model of real estate base on least risk and anticipated profit is studied in the discussion of its concerned hypothesis and determining the concerned parameters. With living example analysis, we reach the conclusion that portfolio investment risk is smaller than single investment if the investor adjusts the tactics of portfolio investment.