Abstract: The local structure and bond-orientational orders in molten salt LiF, KCI, LiF, and LiCI systems have been studied by molecular dynamics simulation. The bond spherical harmonics have been calculated for the computer-generated instantaneuos configurations of the molten salt systems. A new method, i.e. the method of bond spherical harmonics statistics under equal neighbor number N, has been proposed. For the standard structures with different coordination number, their quadratic invariant Q_l histograms under same N have been calculated and a model with a parameter of square deviation have been suggested. Comparing the Q_l from molecular dynamics simulation with the standard Q_l from linear combination of two standard structures, it can be found that the local structures in those four molten salt systems are near to tetrahedron more or less and the icosahedron structure is hardly found. The results showed that the fractions of tetrahedron local structure increase as the ratio r_+/r_- of cation radius r_+ to anion radius r_- decreasing.