Weak epitaxy growth (WEG) behavior and mechanism of copper hexadecafluorophthalocyanine (F16CuPc) on p-sexiphenyl (p-6P) monolayer film were investigated by atomic force microscopy (AFM), selected area electron diffraction (SEAD), and wide-angle X-ray diffraction (WAXD). High-quality F16CuPc films with high order, large size, and molecular-level smoothness were obtained successfully by WEG method. It was identified that there exists incommensurate epitaxial relation between highly oriented F16CuPc and p-6P films. The geometrical channels of p-6P monolayer surface induce the nucleation and growth of F16CuPc molecules. Two kinds of in-plane structures, referred to as "phase I" and "phase II", coexist in the initial few molecular layers. As thin-film thickness increases, the distance of (001) plane diminishes and phase I disappears. Furthermore, coalescence, dislocation, and high-angle grain boundary between F16CuPc neighboring domains were observed by high-resolution AFM.