Establishing the connection between deterministic safety design and reliability design of pile plate structure subgrade, this paper first derives the analytical solution for settlement calculation of pile plate structure subgrade and establishes the reliability analysis model for the subgrade. The influence of the variability coefficient of subgrade soil elastic modulus, upper load, and pile spacing on the failure probability of subgrade settlement is studied. Subsequently, a framework for settlement safety criteria of pile plate structure subgrade based on the generalized reliability ration of safety margin is proposed. The relationship between the relative safety margin of the generalized reliability index and the safety factor’s relative safety margin is analyzed, and the effect of overlying load on the critical pile spacing is discussed. The results show that the settlement calculation method in this paper can better reflect the settlement deformation characteristics of the pile plate structure subgrade. The settlement of the pile plate structure subgrade is jointly determined by the upper load and the combined stiffness of the plate, and its failure probability curve with the load level changes from a steep increase to linear growth as the variability coefficient of the subgrade soil elastic modulus increases. The relative safety margin of the generalized reliability index and the safety factor"s relative safety margin exhibit an approximately linear relationship, and by allowing the failure probability to calibrate the allowable safety factor, the basic consistency of deterministic design and reliability design of the pile plate structure subgrade is ensured. In addition, an increase in overlying load will lead to a logarithmic non-linear decrease in the critical pile spacing.