1. A method of rendering volume data having multi-resolution, the method comprising: dividing the volume data into a plurality of sub-volumes according to a resolution; producing a reference table including a grid structure of the volume data and resolution levels of the plurality of sub-volumes; determining a sampling interval for each of the plurality of sub-volumes, based on respective resolutions of the plurality of sub-volumes, by using the reference table; and sampling sub-volumes present in a path of a ray passing through a pixel on a projection plane onto which the volume data is projected from one viewpoint, according to the determined sampling intervals.