This study presents a strategy which integrates extra polishing path (EPP) and error map extension to weaken the edge effect in the ultraprecise optical surfacing process. Different data extension algorithms were presented and analyzed. The neighbor-hood average can be selected as the frequently-used method, as it has not bad precision and time-saving performance for most surface forms through the simulation results and practical experiment. The final error map was obtained, its peak-to-valley (PV) was 0.273l and root mean square (RMS) was 0.028l (l=632.8 nm). The edge effect was weakened and suppressed well through the experiment.