In order to study the effect of shape on graphene pressure sensors, a theoretical model of polymerisation degree is proposed in this work. According to the theoretical model of polymerisation degree, it is found that the regular polygons have better sensitivity characteristics. The more the number of sides for the regular polygons, the larger the polymerisation degree, and the better the sensitivity of the graphene pressure sensors. According to the theoretical model, the polymerisation degree of the positive triangle, regular quadrilateral, regular pentagon, and circle shape is 0.5, 0.71, 0.81, and 1, respectively. The measured results show that the relative resistance change of positive triangle, regular quadrilateral, regular pentagon, and circle shape are 8.56, 9.24, 9.61, and 10.4%, respectively. The experimental results are consistent with the theoretical results. Therefore, the theoretical model of polymerisation degree can provide effective quantitative guidance for the graphene pressure sensors.