The four-point bending test of 5 groups of recycled aggregate substitute rates and 4 groups of steel fiber reinforced recycled aggregate concrete prism specimens were conducted to study the effects of recycled aggregate substitution rate and steel fiber content on the flexural strength and the scale effect of recycled concrete. The test results show that there is scale effect in the flexural strength of each kind of prism specimens. With the increase of the substitution rate of recycled aggregate, the scale effect of the flexural strength of recycled concrete increases first and then decreases. The scale effect of the flexural strength of the specimen with a substitution rate of 75% is about 1.32 times and 1.09 times that of the specimens with a substitution rate of 0 and 100%, respectively. The content of steel fiber has a certain effect on the scale effect of the flexural strength of recycled concrete. When the steel fiber content ranges from 0% to 0.75%, the larger the content of steel fiber, the more pronounced the scale effect is. The scale effect of specimens with steel fiber content of 0, 0.25% and 0.5% is about 79%, 85% and 94% of the specimen with steel fiber content of 0.75%, respectively. When the steel fiber content is over 0.75%，the variation on the scale effect of flexural strength with different steel fiber contents is limited. The scale effect of the specimen with steel fiber content 0.75% is about 99% of the specimen with fiber content of 1%. A calculation formula for the scale effect law of the flexural strength of recycled concrete is proposed，which can be used to analyze the flexural strength of recycled concrete.