Abstract: The reinforced area and non-reinforced area of a composite foundation are regarded as a whole, the reinforced area is taken as a natural foundation whose compression modulus equals as a composite modulus; the settlement of the composite foundation is computed by means of the layering summation method of a natural foundation. The models for the reliability analysis on the composite foundation settlement based on the Boussinesq’s stress and displacement solution under a vertical concentrated load is established. The effect factors on the reliability index of the composite foundation settlement are analyzed through an engineering example. Considered the function’s non-linear and included integral term, the reliability index computation is difficulty by the checking point method then by Monte-carlo method. Monte-carlo method does not deal with the computation of partial derivatives, and the limit of the function’s non-linear and numerical integral.