Enhancing the diffraction efficiency of continuous-relief diffractive optical elements fabricated by direct laser writing is discussed. A new method of zone-boundary optimization is proposed to correct exposure data only in narrow areas along the boundaries of diffractive zones. The optimization decreases the loss of diffraction efficiency related to convolution of a desired phase profile with a writing-beam intensity distribution. A simplified stepped transition function that describes optimized exposure data near zone boundaries can be made universal for a wide range of zone periods. The approach permits a similar increase in the diffraction efficiency as an individual-pixel optimization but with fewer computation efforts. Computer simulations demonstrated that the zone-boundary optimization for a 6\mathrm{\mu m} period grating increases the efficiency by 7% and 14.5% for 0.6\mathrm{\mu m} and 1.65\mathrm{\mu m} writing-spot diameters, respectively. The diffraction efficiency of as much as 65\%–90\% for 4–10\mathrm{\mu m} zone periods was obtained experimentally with this method.