In terms of the problems of the traditional rigid industrial endoscope, such as small monitoring field, low resolution, and short working distance in the furnace, a high-definition industrial endoscope with large optical format and long working distance is designed. The integrated design is adopted, and it includes an image telecentric objective system with wide angle and a symmetric aberration elimination relay system with the rod lens. The high-definition industrial endoscope is designed as follows. Its optical F-number is 6, the field of view is 103°, the optical length is 1040 mm, the optical outside diameter is not more than 26 mm, the target diagonal is 16 mm, the system image telecentricity is not more than 1.8° and the modulation transfer function is not more than 0.2@160 lp/mm. Experimental results show that the designed industrial endoscope can obtain a clear image in the range from 40 cm to infinity and can resolve the line pair width of 10 mm at a distance of 5 m, with an angular resolution of 8.73 C/(°). The endoscope has advantages in view of design. Specifically, its receiver target surface is large, and the object resolution is high. The symmetric aberration elimination relay system with the rod lens has good ductility and high luminous flux. Objects and images are connected in telecentric form, with smooth light transmission and uniform illumination on the image surface.