The invention provides a lens fixing device. The lens fixing device comprises a lens carrying body, a shell and a sealing cover; a sinking groove for placing a lens is formed in a first side face of the lens carrying body, a first light passing hole is formed in the bottom of the sinking groove, and the sectional area of the first light passing hole is smaller than the bottom area of the sinking groove; a cavity is formed in the shell and used for being provided with the lens carrying body; second light passing holes are formed in two opposite inner walls of the cavity, are parallel to the first light passing hole, and are used for being communicated with a light passing pipeline; the sealing cover is arranged at an opening of the cavity of the shell and used for blocking the opening of the cavity. The lens fixing device is of a full-closed-type structure, it can be guaranteed that the lens and a light path are isolated from the outside, interference of stray light and dust is eradicated, and the requirement of optical equipment for the external environment is lowered.