We conduct a systematical investigation into the short-time stretch relaxation behavior (i.e., shorter than the Rouse time but sufficiently longer than the glassy time) of entangled polymer liquid in single-step strain flows, on the basis of theory/data comparisons for a broad series of type-A entangled polymer solutions. First, within existing normal-mode formulations, the Rouse model predictions on a full-chain stretch relaxation in single-step strain flows are derived for a popular 1-D model proposed within the Doi-Edwards tube model, as well as for the original 3-D model for nonentangled systems. In addition, an existing formula for the aforementioned 1-D model that, however, rested upon a consistent-averaging or the so-called uniform-chain-stretch approximation is simultaneously examined. Subsequently, the previously derived formulas on chain stretch relaxation are directly incorporated into a reliable mean-field tube model that utilizes the linear relaxation spectrum and the Rouse time constant consistently determined from linear viscoelastic data. It is found that the predictions of the 1-D model differ substantially from that of the original 3-D model at short times. Theory/data comparisons further indicate that the 1-D model without approximations seems able to describe fairly well the nonlinear relaxation data under investigation. (c) 2006 Wiley Periodicals, Inc.