Abstract: Coordinate transformation between quarternary triangular mesh (QTM) code and longitude/latitude is one of the main factors in affecting the application of QTM. However, there are significant flaws in the existing algorithms. To overcome this deficiency, an improved transformation algorithm is proposed in this paper. The main principle is as follows:According to the row and column of QTM, the address codes are recursively approached in a certain direction. Then, the transformation results are obtained precisely by introducing the operation of the relation between the judgment point and the line segment. In this algorithm, not only the transformation result is accurate but also time consumption is only about 10.1%-10.4% of equal-triangles projection (ETP) method. In addition, the QTM code obtained in the improved algorithm still has the directionality. The improved algorithm works well for both traditional QTM and the QTM which using latitude-line instead of circle-line.