As one type of high performance fibers, polyimide fibers can be prepared from polyamic acid (PAA) solution by dry-spinning technology. The transformation from the precursor of polyamic acid to polyimides via thermal cyclization reaction in the dry-spinning process is a main distinguishing feature, which is very different from other fibers produced by dry-spinning such as cellulose acetate fiber and polyurethane fiber. In this report, the dry-spinning formation of polyimide fibers with trilobal cross section from PAA solution in N,N-dimethylacetamide is simulated via a one-dimensional model based on a viscoelastic constitutive equation, combined with profile degree equation of cross section and imidization kinetics equation. The glass transition temperature, imidization degree and profile degree of the filament along the spinline are predicted by the model, as well as relative parameters such as solvent mass fraction and temperature. As a simulated result, solidification of polyimide fibers take place about 150 cm from the spinneret which is farther than for cellulose acetate fiber (70 cm). Moreover, the final profile degree of fiber is affected by many spinning parameters, such as spinning temperature, surface tension, spinning solution concentration, major, and minor axis length of the spinneret hole. POLYM. ENG. SCI., 55:2148-2155, 2015. (c) 2015 Society of Plastics Engineers