The karyotyping plays an important role in genetic researches.However,the traditional method of karyo- type analysis is performed with a complicated banding process,and the result is obtained by the visual analysis of operators.The complicated process of sample preparation and the subjective result make the karyotype analysis la- borious and time-consuming.In order to precisely extract the altitude curve that is of great significance for the karyo- type analysis,a new method of extracting the altitude curves along the chromosomes was proposed on the basis of the relationship between the altitude features of human chromosomes and the band structure under optical microsco- py.Then,the chromosomes prepared in air condition were imaged by using an atomic force microscopy,and the al- titude curves extracted through the conventional method were compared with those from the proposed method.Ex- perimental results show that,the proposed method can extract the altitude curves more effectively,and it also achieves a good effect in handling the chromosomes of serious contraction deformation.