Abstract: In this paper the foundamentals,structure,electric circuit system and its application method of the newly designed and manufactured Optic-electric Area-measuring Instrument Type GDM-I are introduced in detail.The following is the working procedure of the instrument:The area to be measured is fixed on the revolving sylinder and scanned,through Optic-electric transformation,amplifying and shaping,the figures are shown on the counter and by simple calculation,the area is thus obtained.The error of measurement is less than 0.5%.An example of area measuring is done for the whole area of a County(in Hubei Province) and its communes and towns,too.The result shows that the measurement is accurate and satisfactory.