The structures in β-BaB2O4(BBO) growth solutions, which are BaB2O4-Na2O binary melts with different molar concentrations of Na2O(12.5%,20%,25%,30%), have been studied by molecular dynamics simulations. The simulated B-O radial distribution functions with different Na2O concentrations show that the first peaks become high and sharp with the increasing of Na2O concentration. Based on the instantaneous configurations given by the simulations, the local structures of the binary melts were analyzed by means of the bond order parameter method combined with the statistics of rings and chains. The results indicate that the adding of Na2O as a flux into the melt systems will make more planar BO3 structure units and more isolated BO3, B2O5 and B3O7 clusters while the network in the melts will be greatly weaken, which are all beneficial to the forming boroxol groups B3O6 and the growing of BBO crystal. The statistics also shows that the percentages of B atoms in isolated BO3 and the percentages of B atoms in long chains are in good agreement with the experimental values of volatility and viscosity of hte solution systems, respectively.