Abstract: This microcomputer method is designed with the Fox model as reference for building 5S Rrna secondary structure.By inputing the nucleotide sequences of 5S Rrna and calculating through the work of the Z-80 microcomputer about 4 minutes,we got the secondary structure with the lowest total free energy,corresponding to the Fox model when only secondary interactions are under consideration.The result is basically in agreement with literature (2,4,5,6,7,8).The method has the advantage of simplicity,low cost and comsuming less time,so,it is a method that can be easily popularized.