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Coarse-grained(CG)and all-atom(AA)molecular dynamics(MD)simulations are proposed to investigate the packing behavior of a semiconducting conjugated polymer,poly(3-alkylthiophene)(P3AT)in the ordered state.We adopt the iterative Boltzmann inversion method to obtain CG force-field parameters through mapping route with the AAMD data.We have modified both interactions of dihedral angle and inter-pair potential between the thiophene rings by considering the polarity effect and π-π interaction.The modified CG potentials have been successfully and efficiently employed to investigate the self-assembling behavior of P3AT molecules in the ordered state.Besides,we systematically examine the effects of grafting density and length of alkyl side-chains on the phase behavior of P3AT polymers.The single-layered lamellae,double-layered lamellae,disorder,double-layered lamellae/honeycomb have been obtained at the grafting density of 100%,50%,33%,and 25%,respectively.With increasing the length of side-chains,the flexible side-chain disrupted the rigidity of main-chains to form fragmented lamellae or disordered phase.Our simulation results have successfully illustrated the significant effects of grafting density and alkyl side-chain length,polarity of thiophene rings and π-π interactions along main-chain direction on the self-assembling behavior of P3AT polymers.