During the operation of fishing with light at sea, rolling motion of the fishing boat changes the illumination angle of the light-emitting diode (LED) fishing lamp, resulting in continuous changes of the sea surface illumination, which has an adverse effect on attracting and gathering phototactic fish. This article proposes a method using a free-form surface lens to realize a fan-shaped light intensity distribution, with the divergence angles on the X-Y and Y-Z planes being 110° and 10°, respectively. The similarity and error rate of the relative illuminance distribution of the target plane within the illumination angle range of -10°--10° were analyzed. The normalized cross correlation (NCC) of the simulation results and the experimental results are greater than 98.50% and 99.53% respectively, and the root mean square error (RMSE) are less than 5.56% and 4.60%, correspondingly. By comparing this design with a standard LED fishing lamp and metal halide lamp, the results show that the proposed design significantly improves the illumination stability of the LED fishing lamps when the fishing boat rolls, indicating that the free-form surface lens is able to provide stable illumination on the sea surface at different illumination angles.