•The turning function provides a new method for geometric morphometry and a new perspective for the study of pottery morphology.•This study is the first to publish the results of classifying the pottery unearthed at the Gansu-Ganguya site.•The method of obtaining pottery model by photogrammetry is introduced in detail. Geometric morphometry is a method used to analyse the morphological characteristics of research objects and has many applications in biological analysis. With the development of 3D digital technology, geometric morphometry is widely used on 3D models. The pottery samples were obtained from the Ganguya site (1850 and 1500 BCE) in Gansu Province. Three-dimensional models of the pottery were obtained by photogrammetry, and the outline curves of the pottery were extracted. The outline curves were converted into angles by a turning function, and four characteristic indices were extracted according to the features of the angle function curve. Two principal components were extracted, and the samples were divided into three categories by the K-means clustering algorithm. The characteristics and differences of the three categories were analysed. The turning function provides a new method for generating an outline in geometric morphometry and a new perspective for the study of pottery morphology.