Based on the liquid crystal/polymer grating and with MDMO-PPV as the gain medium, the emission wavelengths at different positions of the gain medium layer can be roughly modulated and then precisely tuned by applying an external electric field. A continuous fine-tuning organic semiconductor laser with a tuning range of 18 nm is finally obtained based on the liquid crystal/polymer grating. This study provides some new ideas for the improvement of a tunable distributed feedback (DFB) organic semiconductor laser.