The invention discloses an optical system of a depth camera. The optical system comprises six lenses that are arranged successively along the optical axis from object space to image space. The first lens has a crescent shape with a negative focal power and a convex surface of the first lens faces the object space; the second lens has a crescent shape with a negative focal power and a convex surface of the second lens faces the object space; the third lens has a biconvex shape with a positive focal power; the fourth lens has a biconcave shape with a negative focal power; the fifth lens has a biconvex shape with a positive focal power; and the sixth lens has a biconvex shape with a positive focal power. According to the optical system of the depth camera, with different lens combination units and focal-power distribution, excellent performances of large aperture, large view angle, and low distortion are realized; and on the basis of the glass-plastic mixing structure, athermalization and low manufacturing cost can be effectively considered.