The annihilation of dark-matter particles may lead to the production of monochromatic gamma-ray emission. In this contribution, the search for spectral lines in the gamma-ray spectrum using nine years of data collected with the space-borne Dark Matter Particle Explorer is presented. No line signal is found between 5 GeV and 1 TeV in several regions of interest. The constraints on the velocity-averaged cross section of the neutralino annihilation are estimated for different dark-matter density profiles and compared with other experiments on ground and in space.