Ultra-high performance concrete (UHPC) prismatic specimen with different water-binder ratios, coarse aggregate contents, steel fiber volume fractions, and specimen dimensions were prepared. The influences of water-binder ratio, coarse aggregate content and steel fiber volume fraction as well as the scale effect on the flexural tensile strength of UHPC containing coarse aggregate were investigated. The results show that the flexural tensile strength of UHPC containing coarse aggregate decreases with the increase of the water-binder ratio and the coarse aggregate content. The scale effect on the flexural tensile strength of UHPC containing coarse aggregate is greater than that of UHPC without coarse aggregate. The scale effect on the flexural tensile strength of UHPC containing coarse aggregate decreases gradually with the increase of water-binder ratio. The scale conversion coefficient of flexural tensile strength of UHPC containing coarse aggregate and the parameter calculation formula of scale effect law were proposed for predicting the flexural tensile strength of UHPC with coarse aggregate.