A multi-scale simulation approach was proposed to predict the degree of impregnation (Dol) in thermoplastic unidirectional carbon fiber prepreg (UD-CFP). The multi-scale approach included a two-dimensional (2D) micro-scale computational fluid dynamics (CFD) in a representative elementary volume (REV) of carbon fiber (CF) tow, a 3D macro-scale CFD of an entire impregnation die with 15 sliding CF tows, and a process-scale simulation assembling data from the micro- and macro-scale CFDs. In the macro-scale steady-state CFD, thermoplastic resin injection and CF tow insertion were considered for an impregnation die 10 cm in width. In the micro-scale transient CFD, impregnation mechanisms of resin into CF filaments 7 mu m in diameter were identified in terms of surface coverage, capillary permeation, and penetration through CF filaments. The Dol as a function of pressure and time was obtained from the micro-scale CFD within a range of pressures found in the macro-scale CFD. In the process-scale simulation, the cumulative Dol of the 15 tows was predicted along the impregnation die length with the aid of the micro- and macro-scale CFD results. Combining the multi-scale models gives a potential to predict the uniformity of the transverse resin amount in the final UD-CFP product. (C) 2018 Elsevier Ltd. All rights reserved.