Incomplete studies exist on the identification and formation processes of lunar cryptomaria, which stand as crucial hubs of late lunar magma ocean activity and early volcanism, presenting a mystery in their orgin. Here, we show 29 delineated cryptomaria regions, based on remote sensing data. A thorough investigation of gravity anomalies within these proposed cryptomaria regions was undertaken. Through this analysis, we successfully identified and classified cryptomaria by integrating topographic features and chemical compositions. Our findings reveal that the formation of ancient cryptomaria is linked to large impact events. This establishes a clear correlation between impact events and the formation timeline and spatial distribution of cryptomaria. Older cryptomaria owe their existence to these impact events, while the younger cryptomaria is primarily located in the interiors and margins of maria, with their basalts originating from the lateral spread of these maria. Furthermore, the study of maria thickness remains a contentious subject, and we anticipate that forthcoming investigations, consolidating data from various sources, will ultimately resolve this matter.