A design method of the single-chip capsule endoscope with harmonic diffraction surface is introduced with the system working band of 0.486~0.656 μm and the field-of-view angle of 116.2°. And the total length of the optical system is 2.4 mm. Additionally, a capsule endoscope with three spherical lenses and a single-chip capsule endoscope with aspherical surface are designed, and a comparison is made between them and the single-chip capsule endoscope with harmonic diffraction surface. It is found that the single-chip capsule endoscope with harmonic diffraction surface can achieve the image quality of the capsule endoscope with three spherical lenses. and its construction is as simple as the single-chip capsule endoscope with aspherical surface. Its modulation transfer function is greater than 0.6 at the frequency of 40 lp/mm.