By changing the Rabi frequency of the photoassociation laser and the atom-polymer coupling strength, we investigate the effect of external field shape on atom-polymer conversion efficiency. First, by defining time-index, the external filed shape given in literature is improved. We discuss the influence of time-index on conversion efficiency, and then choose a more optimized external filed shape, it has good parameter robustness. Under the action of the external field, the adiabatic process has almost no oscillation, the adiabatic fidelity is close to 1, and the error of the system is less. The ultracold atom-polymer molecules conversion can be realized stably and efficiently.