Development of the nano-electronics requires materials with both high carrier mobility and a sufficiently large electronic band gap.In this work,by means of ab initio calculations,we have predicted a new 2D Ca2Si monolayer with a quasi-planar hexa-coordinate structure.The geometrical structure,stability and electronic properties ofCa2Si monolayer have been systemically investigated.The Ca2Si monolayer is an indirect semiconductor with band gap of about 0.77 eV,which exhibits stable chemical bonding interactions as well as thermal and dynamic stability.Moreover,the carrier mobility in Ca2Si monolayer is electron dominated with a high electron mobility about 4590.47 cm2.V1.s-1.It is excited that the 2D Ca2Si monolayer exhibits strong directionally anisotropic carrier mobility,which could effectively facilitate the migration and separation of the generated electron-hole pairs.Our calculations demonstrate that the 2D Ca2Si monolayer is potential for high efficiency solar cells and other nano-electronic applications.