This invention relates to a method of creating a complex curved surface, which includes a step of from data specifying three-dimensional curved surfaces (12a, 12b). Data is input specifying a reference line of intersection (CL.sub.i) on the XY plane (10) and a rule for generating lines of intersection on the XY plane on the basis of the above-mentioned reference line of intersection. Also a range (SCR1, SCR2) is specified for each of the three-dimensional curved surfaces (12a, 12b) to obtain a section curve on the three-dimensional curved surface, for a section corresponding to one of the lines of intersection. The method includes obtaining first and second section curves (13a', 13b') in the range (SCR 1, SCR2) when first and second three-dimensional curved surfaces (12a, 12b) are cut by a section whose line of intersection with the XY plane is an i-th line of intersection (CL.sub.i). Then, a point of intersection (CR.sub.i) between the two section curves (13a', 13b') is obtained. Thereby, a set of first and second section curve segments A1 - CR.sub.i, CR.sub.i - B2), having the point of intersection (CR.sub.i) as a boundary, are used to define a section curve of the complex curved surface (11). The complex curved surface (11) is generated from sets of these section curves.