The process of layered Additive Manufacture (AM) limits manufactured parts, which leads to the stair-step error, support structures and the anisotropy. CLFDM has been proposed by researchers to alleviate these problems. However, to the best of our knowledge, available CLFDM mainly focuses on filling with the uniform extruded filament in the same layer. While intricate parts usually possess small and critical features, as well as manufacturing error and assembling error. Geometry accuracy and mechanical property of Fused Deposition Modeling (FDM) parts are closely related to inter-layer and inter-road bonding. Therefore, inspired by non-uniform layers of the onion, this paper pays attention to CLFDM with VEF in the layer and between adjacent layers innovatively, whereby the direction and dimension of extruded filament are variable. The literature review of slicing and path planning is given first to make readers better understand the current status and the research gap to highlight the innovation of this paper. Then, flat layer FDM and CLFDM with VEF are modeled respectively, from the aspect of inter-layer and inter-road bonding. After that, the relationships among key process parameters are analyzed. Finally, the simulation is provided to verify the effectiveness and advantages of our method from a theoretical point of view. Generally, this research can be a foundation for CLFDM with VEF, and the preliminary research has shown broad applications.