Abstract: With excellent mechanical characteristics, polyimide (PI) film is getting more and more attentions in the research area of space structures. This study innovatively used PI fiber to reinforce the PI film. The obtained PI composite film exhibits excellent mechanical properties. When 20 fibers are introduced every cm, the fiber volume fraction of the composite film is only 8.689%, the tensile strength of the PI composite film is increased by 203% and the Young’s modulus is increased by 202% than that of the pure film. With the addition of fibers, the Poisson’s ratio in the perpendicular direction of the PI composite film continues to decrease. The composite film behaves as an orthotropic material. In addition, the mechanical properties of the composite film calculated with the rule of mixture (ROM) and simulated using the finite element analysis (FEA) method are corelated very well with the experimental results.