Based on the classical electrostatic theory, the model of dipole-dipole interaction of rod-like amphiphilic molecules in Y-type Langmuir-Blodgett (LB) film is presented in the paper. The relations between the structure and spectral absorption peak of LB films were obtained by using this model. For Y-type films, the relationship of molecular aggregation state and the structure parameters, i.e. molecular separation distance a, separation d between two adjacent layers, molecular tilt angle θ, and layer number　g, were studied using our model. Then we compared the similarities and differences of aggregation behavior between Y-type and Z-type films. The theoretical results agree well with experimental data.