Although experimental studies have demonstrated the feasibility of processing glass materials via selective laser melting (SLM), further precise SLM manufacturing of fused silica remains a challenging but promising field. Consequently, a reliable simulation model was developed to predict the densification kinetics of glass powder monolayer under SLM, consequently providing a simulation tool for optimising processing parameters. To be particular, the relative neck diameter and density of the powder bed under SLM were estimated using a cluster model to predict the degree of consolidation, from which the thermal diffusivity of the powder bed can be determined and the corresponding result of heat transfer can be obtained. The experimental observation from other studies supported the numerical results. Therefore, the validated numerical simulation can assist researchers in discussing the effects of processing settings on silica glass under SLM. For instance, using powders with smaller particle sizes and a preheated working environment can improve the quality of the manufactured parts. Based on this model, a novel optimisation criterion can be used to optimise the parameters and fabricate transparent and high-purity glass parts via SLM.