Abstract: In order to study the relationship between the tensile and compressive strength of the concrete commonly used in engineering and the size of specimen, a statistical model of the size effect on concrete strength was established based on the generalized weakest chain formula proposed by Lei recently, assuming that the distribution of the internal defects in concrete follows the uniform distribution or the Poisson distribution. It realizes the prediction of the strength of small-scale concrete specimens to the strength of full-scale members under the condition of a given failure probability. The analysis of concrete strength data from the three published cases shows that: Under the assumption of uniform distribution of defects, the statistical method of size effect can well reflect the relationship between the tensile strength and size of ordinary concrete and RPC.The internal defect distribution of RPC concrete is closer to a uniform distribution, and the relationship between its compressive strength and size can also be described by the statistical method of size effect.