Rheologic filling of semi-solid alloy melt is defined as a process in which the semi-solid slurry poured into a die chamber is pressed into a mold cavity through a filling system including three basic units such as sprue

runner and ingate by means of the rheologic properties of semi-solid alloys. The filling process is composed of active rheology and passive rheology

possibly forming uniform filling and discretely filling. The discretely filling phenomen were observed with the pressure Pm in cavity more than cohesive force τ acted on the solid. Maximum filling length is dependent on cooling capacity of mould

microstructure and reheology of semi-solid slurry through theoretical analysis of origination of rheologic filling resistance and quantitative calculation equation. The evaluation equation for maximum filling length in gyroidal mold was given.