A LED fish aggregation lamp is important equipment in the fishing industry, and it plays a role in attracting and gathering fish. To enhance the overall cooling performance of the lamp, reduce the chip temperature and the heat sink mass, and increase the lifetime of the lamp, we design and optimize the heat sink structure. The computational fluid dynamics (CFD) method is used to simulate the heat transfer performance of the heat sink, and three types of heat sink are analyzed. The results show that heat sink III is the most ideal. Then, an orthogonal experimental design (with four factors and four levels) is used to study the effects of the length, thickness, and spacing of the fins and the semicylinder spacing (four factors) on the cooling performance of the heat sink. When only the chip temperature is considered, the test data show that the optimal level combination is A4B4C2D4 (A, B, C, and D are four factors, and the numbers are the levels of each factor). When both the chip temperature and the heat sink mass are considered, the optimal level combination is A3B2C2D4. The results show that the combination A3B2C2D4 is the best when the maximum chip temperature is 66.49 ℃ and heat sink mass is 3.16 kg.