Recently, high-temperature superconductivity (HTSC) is found in the La3Ni2O7/SrLaAlO4 ultrathin film with critical temperature Tc above the McMillan limit at ambient pressure (AP). It is eager to enhance Tc of La3Ni2O7 at AP. We propose that a perpendicular electric field strongly enhances Tc in the single-bilayer film of La3Ni2O7 at AP. Under electric field, the layer with lower potential energy will accept electrons flowing from the other layer to fill in the Ni- 3 d x 2 − y 2 " role="presentation" style="box-sizing: inherit; display: inline-block; line-height: normal; font-size-adjust: none; word-spacing: normal; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;"> orbitals, as the nearly half-filled Ni- 3 d z 2 " role="presentation" style="box-sizing: inherit; display: inline-block; line-height: normal; font-size-adjust: none; word-spacing: normal; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;"> orbital cannot accommodate more electrons. With the enhancement of the filling fraction in the  3 d x 2 − y 2 " role="presentation" style="box-sizing: inherit; display: inline-block; line-height: normal; font-size-adjust: none; word-spacing: normal; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">  orbitals in this layer, the interlayer s-wave pairing is suppressed, but the intralayer d-wave pairing in this layer is strongly enhanced. We numerically verify this idea and yield that an imposed voltage of about 0.1 ~ 0.2 volt between layers is enough to realize liquid-nitrogen-temperature HTSC in this single bilayer at AP. Our results appeal for experimental verification.