The invention discloses a method for achieving cross-scale photolithography or multi-resolution imaging through change of a beam expansion ratio. A beam expanding mirror in a single-beam spot scanningphotolithography or imaging system is replaced with an electric adjustable magnification beam expanding mirror, and then according to a relevant calculation formula, continuous adjustability of the diameters of focal spots is achieved through adjustment of the beam expansion ratio. According to the method, the spots with the continuously adjustable diameters can be provided in the single-beam spot scanning photolithography or imaging system, and the cross-scale photolithography or multi-resolution optical imaging can be achieved rapidly, simply and conveniently.