Nanomanufacturing can be further classified as nano precision manufacturing and nano scale manufacturing. Typical examples include nano mechanical machining to realize complex forms in nano precision and focused ion beam fabrication to realize various features in nano scale. To better design and control nano mechanical machining process, it is vital to understand the fundamental mechanism. Since the atomistic details of manufacturing process are difficult to obtain by experiments, molecular dynamics (MD) simulation as a simulation method has been widely used to study the machining mechanism. However, the length and time scales that MD can probe are still limited, which prevent MD from modeling the real machining process as it generally involves in nano, micro and macro scales. Therefore, it is essential to develop multiscale method coupling nano, micro and macro scales. This keynote speech overviews the previous multiscale simulations and particularly present a 3D multiscale model to study the nano machining process. The model consists of a single crystal silicon workpiece and a rigid diamond tool. In the critical region around the tool, there are large strain gradients and thus the molecular dynamics is employed. While in the “far-field” region with small strain gradients, Linear elastic FE is adopted. MD and FE are coupled through a handshake (HS) region where MD atoms and FE nodes overlap. Each provides boundary conditions for the other at the edge of the HS region to realize the concurrent multiscale study. Machining of optical freeform elements is presented as the application. The fundamentals of focused ion beam fabrication is also reported as the typical nano scale manufacturing process. As an application of nano scale fabrication, nano optics is discussed, which is the study of the behavior of light on the nanometer scale. A wide variety of novel optical properties would appear in nano-optics, such as, strongly enhanced light transmission, beyond diffraction limitation, etc. With the rapid development of nano-optics, surface plasmon based nano optical elements development have attracted extensive attention, which can be used in the surface plasmon interference nanolithography, plasmon-enhanced sensing and spectroscopy, and super focusing on the nanoscale, etc.