To investigate the effects of light color, power, depth of LED underwater fishing lamp and seawater chlorophyll concentration on its light field distribution, a new underwater light transmission model was established based on Monte Carlo algorithm. The underwater light field distribution under different conditions was calculated by using the control variable method and the relative effective illumination range (REIR). The ratio of the area surrounded by the 0.1-10.0 lx isoline to the computational domain was taken as an evaluation index. With REIR for index, light filed distribution under the combined condition of was analyzed. The results showed that:(1) Under the same light power, the lights with REIR from high to low were green light, white light and blue light, and when the light power was 420 W and the seawater chlorophyll concentration was 0.1 mg/m³, the ratio of REIR values of the three light colors was 1.58:1.31:1; (2) Under the same light color, when the seawater chlorophyll concentration was 0.1 mg/m³, the power of fishing lamp increased from 420 W to 1200 W, and the REIR value of blue, green, and white light lamp increased from 31.68%, 50.27% and 41.78% to 38.59%, 56.91% and 50.15% respectively; while the power of lamps increased nearly three times, the increase of REIR was limited; (3) As the depth of lamp increased, the REIR of lamps increased at first and then kept stable. The maximum value of green and white lamp was about 9.69%-9.84% when the depth of lamp reached 20 m under water, while the maximum value of blue lamp was about 5.60% when the depth of lamp reached 15 m under water; (4) As the chlorophyll concentration increased from 0.1 mg/m³ to 5.0 mg/m³, the REIR value of green, white and blue lamp decreased from 31.89%, 48.25% and 42.05% to 1.65%, 2.09% and 2.22% respectively. The results can be helpful for the selection of light color and power, the depth of underwater lamp, and the estimation of effective illumination range of lamp.