Abstract: Abstract: In this paper, a three-dimensional CFD numerical model of heat transfer and fluid flow was developed to simulate the thermal performance of the novel flat plate solar collector based on a micro heat pipe array to provide a theoretical basis for the structure improvement and optimization of the collector. The simulation of the novel collector with water flow included the CFD modeling of solar irradiation and the modes of mixed convection and radiation heat transfer between the absorber plate and glass cover, as well as the heat transfer in the circulating water inside the heat exchanger and conduction of the insulation. The fluid flow and heat transfer in the computational domain satisfied the continuity equation, the momentum equation, and the energy equation. The standard k-ε two-equation turbulence model was used in this paper. In order to predict the direct illumination energy source that results from incident solar radiation and the radiation field inside the collector, the discrete ordinate radiation model with a solar ray-tracing model was used. A commercial computational fluid dynamics program (Fluent 6.3 CFD software) was used to solve the coupled fluid flow, heat transfer, and the radiation equation. The solver used is the segregated solver. Body Force Weighted was selected as the discretization method for pressure, and the SIMPLE algorithm was used to resolve the coupling between pressure and velocity. The discretization methods for the solving of momentum, energy, radiation, and turbulence were second order upwind. The thermal performance could be achieved by simulation results under different conditions. Then, the experimental and numerical results were compared to validate the prediction of the CFD model. The results showed that the numerical results of the thermal efficiency of the novel collector were in reasonable agreement with the experimental data.The validated CFD model was used to analyze the properties of the insulation layer. First, the effects of the thickness of solid insulation on the thermal performance of the collector were simulated using the numerical model. It indicated that when the thickness of solid insulation was 0.02, 0.03, 0.04, and 0.05W/(m·K) respectively, the optimum thickness of solid insulation was respectively 4.5, 5.0, 5.5, and 5.5 cm respectively. Then, in order to save cost, a new concept of the hollow insulation was presented on the insulation design of the collector, namely the combination of an air layer and a solid insulation layer. The simulations were conducted for the collector with a different size of the hollow insulation. The thermal efficiency comparison results of the collector for the hollow insulation and the solid insulation resulted in the following conclusions: 1) When the thickness of insulation was 4cm, the collector of hollow insulation with combination of 2 cm air layer and 2 cm solid insulation could get the same thermal performance as the solid insulation. And 25%-50% of the cost and weight of the insulation were saved. 2) When the thickness of insulation was 5cm, the collector of hollow insulation with combination of 2 cm air layer and 3 cm solid insulation could get the same thermal performance as the solid insulation. And nearly 40% of the cost and weight of the collector were saved. 3) When the thickness of insulation was 6cm, the collector of hollow insulation with combination of 3 cm air layer and 3 cm solid insulation could get the same thermal performance as the solid insulation. Nearly 50% of the cost and weight of the insulation were saved. Therefore, a reasonable design of the hollow insulation could obtain the same resemblance thermal insulation effect as the solid insulation collector, but the cost and weight could decrease from 25%-50%.