The invention provides a method for computing angles of unmanned aerial vehicles and a method for applying the method for remotely measuring gas. The method for computing the angles of the unmanned aerial vehicles includes steps of (A1), photographing the flying unmanned aerial vehicles from locations below the unmanned aerial vehicles so as to obtain images of the unmanned aerial vehicles; (A2), acquiring symbolic graphics in the images by the aid of Hough transformation algorithms; (A3), acquiring the angles of the unmanned aerial vehicles according to the locations of the symbolic graphics in coordinate systems. The methods have the advantages of short time consumption, high precision and the like.