Abstract: The three-dimensional lattice structure technology is an innovative technology with both lightweight and function-structure integrated design.The selective laser melting technology for lattice structure forming faces serious size effect problems when forming cross-scale structures and gradient structures，which restricts the application and promotion of lattice structure.The “shape” and “performance” of the characteristic structure are important criteria for evaluating the printing quality.Therefore，taking the characteristic structure of three-dimensional lattice-struts and thin walls as the research objects，the relevant researches on size effect are systematically reviewed.Firstly，basing on the analysis of temperature field，this paper expounds the influence law of characteristic size on macroscopic heat accumulation and mesoscopic melt pool size，temperature gradient and cooling rate，which provides a basis for further “shape” and “performance” analysis.Secondly，defects and microstructure morphology are the main content of controlling “shape”.Therefore，the influences of characteristic size on three kinds of defects degree (microporosity，dimensional accuracy and roughness)，as well as two kinds of microstructural characteristics (grain size and orientation) are summarized，and the forming mechanism is analyzed.Finally，the influences of different defects and microstructure characteristics on the mechanical properties are compared to provide reference for the control of “performance” for the lattice structure.The research work of some scholars also shows that reasonable process parameter selection for specific feature size can effectively improve the printing quality and mechanical properties of the feature structure，which provides a reference for the process design of cross-scale structures and gradient structures，and also sparks inspiration for the exploration of extreme lightweight.

Key words: size effect, selective laser melting, lattice structure, characteristic size, porous structure