Molecular dynamics (MD) simulations were employed to investigate the interactions between polyether polyamino methylene phosphonate (PAPEMP) with different degrees of polymerization (n = 1-7) and (010), (020) crystal surfaces of anhydrite. An aqueous environment was added through the introduction of water in the simulation cell. The results showed that PAPEMP molecules attach to the surfaces rather than remain in the bulk water and the interactions of the same PAPEMP molecule with the two surfaces show small differences; under the same mass of PAPEMP (n 1-7), the order of the binding energy E-m of PAPEMP is as follows: PAPEMP (n = 3) > PAPEMP (n = 2) > PAPEMP (n = 1) > PAPEMP (n = 4) > PAPEMP (n = 6) > PAPEMP (n = 5) > PAPEMP (n = 7). The number of the functional groups and the stereo-hindrance effect are two main factors influencing the interactions between PAPEMP and anhydrite. When n <= 3, the former is the main factor; while n > 3, the latter is the main factor. The binding energies are mainly provided by the ionic bond and the non-bonding interaction. The structures of the polymers are deformed during the combining processes. Simulation results provide theoretical guidance to judge the performance of scale inhibitors, and synthesize new highly effective scale inhibitor. (C) 2013 Elsevier B.V. All rights reserved.