Creep age-forming combined creep and precipitation strengthening on aluminum alloy is an advanced integrated panel forming technology in the aerospace industry, and has been widely studied. The interaction between precipitation and dislocation creep in7xxx series aluminum alloy significantly affect on stress relaxation behavior, which decides the forming quality and properties of integrated panel, during age-forming process, since 7xxx series aluminum alloy as a typical age-hardening alloys. In this paper, the effect of different size precipitates on stress relaxation behavior of 7050 aluminum alloy during age-forming process has been investigated, which is helpful to apply creep age-forming technology of 7xxx series aluminum alloy with different tempers. The precipitates can obstruct dislocation thermal activation, therefore 7050 aluminum alloy with different size precipitates obviously exhibits different stress relaxation behavior, and relaxation rate decreases and relaxation limit increases with increasing precipitates size respectively. The calculation of dislocation activation volume and microstructure characterization proves that the obstruction to dislocation motion from precipitates improves with increasing precipitates size. Besides, a special threshold stress phenomena was present in the stress relaxation of the age-forming process, which was scribed to the interaction between precipitation and dislocation in 7050 aluminum alloy.