The invention relates to a scanning mirror assembly for a double scanning infrared earth sensor. The scanning mirror assembly comprises a reflecting mirror and a base, wherein the reflecting mirror comprises a metal mirror and two installation lugs, the metal mirror has an asymmetrical V-shaped structure, two V-shaped surfaces (a, b) of the V-shaped structure are reflecting surfaces, a center position of a shape surface c on the top end of the V-shaped surface a is provided with an alignment reticule 7, a center position of a shape surface d on the top end of the V-shaped surface b is provided with an alignment reticule 11, the two installation lugs 6 are symmetrically arranged on the metal mirror 1, center positions on the upper surfaces of every installation lug 6 are respectively provided with an alignment reticule (12, 13), the surfaces of the shape surfaces excluding the shape surface a and the shape surface b in the V-shaped structure of the metal mirror 1 are black anode oxidation surfaces, and a counterweight groove 2 is arranged on the metal mirror 1 so as to ensure positioning of gravity center of the reflecting mirror on a geometric center line 9. The scanning mirror assembly has characteristics of simple structure, small size, light weight, high reflectivity, stray light interference resistance, space radiation resistance and uniform inertial mass distribution.