Land consolidation is a crucial strategy for optimizing land use structure and ensuring cultivated land security and food safety. Since 2019, Zhejiang Province has been piloting and exploring Whole-Region Comprehensive Land Consolidation (WRCLC). However, there remains an insufficient understanding of the feasibility of WRCLC in ensuring cultivated land security and its potential for synergy with other policies. This study utilizes panel data from 707 townships in Zhejiang Province spanning from 2013 to 2022. By categorizing cultivated land security into two dimensions—quantity and quality—this study employs a double machine learning approach to evaluate the impact of WRCLC policies on township cultivated land security. The results indicate that implementing WRCLC significantly enhances both the quantity and quality of cultivated land. A heterogeneity analysis reveals that WRCLC is particularly effective in improving the quality of cultivated land in non-major grain-producing areas and low economic development areas. Furthermore, examining policy synergies indicates that agricultural mechanization and agricultural industry integration policies work well in conjunction with WRCLC, thereby enhancing both the quantity and quality of cultivated land. However, the synergy with rural tourism policies improves cultivated land quality without effectively increasing cultivated land quantity.