By virtue of a functional scaling, the free energy for cytoskeletal microtubule (MT) solution system in the gravitational field has been proposed theoretically, and on this basis the influence of gravitational field on MT’s self-organization process is studied. A concentration gradient coupled with orientational order characteristic of nematic ordering pattern formation is the new feature emerging in the presence of gravity. Theoretical calculation results show that gravity facilitates the isotropic to nematic phase transition, which is reflected in a significantly broader transition region and the phase coexistence region increases with increasing g or MT concentration. We also discuss the numerical results obtained due to local MT concentration changing with the height of the vessel and some phase transition properties.