Abstract: In this Paper,an experiment on a small computer for making orthophoto maps by the method of digital rectification is described.The main characteristics of this experiment are:1,the fiducial marks are searched automatically by the computer for the inner orientation;2,the terrestrial coordinate system has been turned with an angle k,thus the requirement for the computer memory is reduced;3,measure are taken to considerably simplify the computation of the collinear equation and the bilinear interpolation formula.Experimental results have shown that digital rectification can be used for producing high quality large scall orthophoto maps in mountainous area.