A novel heat-release structure with slotted plate is proposed to enhance the heat dissipation performance of high power multi-chip chip-on-heatsink (COH) LEDs. The junction temperature, thermal resistance, fluid field and the performance of heat dissipation are simulated and analyzed by Icepak software under natural convection. The simulation results show that the slotted plate can improve the flow feature of fluid field, increase the surface heat transfer coefficient, enhance the capability of heat dissipation. There is a best pitch between two plates to make the junction temperature and thermal resistance lower under the thermal conduction and thermal convection. And the junction temperature and thermal resistance lower 3.2 K and 1.01 K/W respectively when the input power of each chip is 1 W under the best pitch. For slotted plate, the capability of heat dissipation is enhanced obviously with the increasing of input power for each chip, and it also decreases the weight of plate and reduces the cost.