In order to master the influence of differential settlement on the quality of cast-in-place beam, the finite element software ABAQUS is used to simulate the stress and strain of the early age concrete beam members under different ages and different settlement conditions. The maximum allowable difference in the quality of cast-in-situ beam in prefabricated soft foundation is given. The results show thatwhen concrete is subjected to excessive uneven displacement load in its early age, plastic zone will appear the cast-in-place beams, which will cause great harm to the quality of prefabricated beams. When the ultimate compressive strain is used as the criterion, the maximum uneven settlement of the structure is 12mm at 1 day, and it is 14mm after 2 days, 14 mm after 3 days, 15 mm after 7days. The maximum uneven settlement at 28 days is 17mm. Therefore, the quality of cast-in-place beams caused by differential settlement of soft soil can be effectively controlled by foundation treatment before the construction of prefabricated beams.