To study and compare mechanical properties and machinability of the polyetheretherketone and the glass fiber-reinforced polyetheretherketone and analyze the relationship between the two properties, nano-indentation experiments and single-point diamond turning experiments were carried out in this article. Through nano-indentation experiments, several material characteristic parameters such as elastic modulus, hardness, and load-displacement data were obtained and load-displacement curve was drawn. It was found that the glass fiber-reinforced polyetheretherketone has higher elastic modulus and hardness but poor uniformity. By single-point diamond turning experiments, two circular planes whose materials are polyetheretherketone and glass fiber-reinforced polyetheretherketone, respectively, were machined. It was found that form accuracy (PV) and surface roughness (Ra) of the former were smaller than those of the later, and glass fiber-reinforced polyetheretherketone plane has poor machined quality. Mechanical property, including uniform structure, stiffness, and resistance to deformation, has higher influence on machining quality.