To address the issues of inconsistent machining results on surfaces of both sides of a gear tooth slot and the lack of controllability over topological modifications on both sides in traditional double-sided form-grinding method (TDFGM), an improved double-sided form-grinding method is proposed. The improved method can ensure the topological modification effect on surfaces of both sides of the gear tooth slot while also maintaining machining accuracy. Based on the theory of gear form-grinding, the contact condition equation between form-grinding wheels and gears is established. According to the mapping relationship between additional motion parameters and tooth surface topological modifications, detailed additional multi-axis motion trajectory design for the improved method is provided. Experimental results indicate improved methods address issues of helix slope deviation present in TDFGMs. Through an analysis of error sources, the contact line morphology is identified as the primary optimization target. A contact line morphology optimization method based on simulated annealing algorithm is proposed. After optimization, gear machining results show profile slope deviations are reduced by 60% on average. Improved method enhance the practicality of double-sided form-grinding in gear modification manufacturing.