The influence of process parameters, including casting temperature, gas flowrate, vacuum level and gas pressure, on the filling ability of A356 aluminium alloy in expendable pattern shell casting process with vacuum and low pressure (EPSC-VL) was investigated in moulds of different thicknesses. It was found that the effect on the filling ability of A356 alloy is in the following order (from strong to weak): gas flowrate, casting temperature, gas pressure and vacuum level. The filling length was found to increase with the increase in all the process parameters, and the relationship between the filling length and the process parameters is almost linear. Moreover, the EPSC-VL process is shown to have advantages in filling ability and internal quality compared with expendable pattern shell casting under gravity and lost foam casting. A high quality complex thin walled part has been successfully produced using the EPSC-VL process.