Substantial efforts have been devoted to investigating the effects of urban form on fundamental natural and social patterns. Such efforts, however, focus mostly on the urban and regional scales. Despite fine-scale investigations that have been conducted recently to analyze how the urban landscape influences urban vitality at the local scale, these studies are often based on the two-dimensional shape of spaces and ignore the diversification of economies and activities in various cities throughout the day. This work examined the relationships between multidimensional urban form and urban vitality at the street block level and explored their variations across fifteen megacities in China. Based on the framework of Conzen’s town-plan analysis, multidimensional urban form was quantified from three fundamental aspects: city plan, building forms, and land utilization. The local vitality was measured in social and economic dimensions at different times of day using restaurant data and nighttime lights. Our results revealed the time- and place-varying relationships between urban form and urban vitality and indicated the successes and failures of widely accepted norms of a good city form. In particular, connectivity, compactness, building arrangement, iconic buildings, transport facilities, and open and green spaces were found to be important for urban vitality, whereas land-use mixture and building density presented limited or unintended effects. Furthermore, some urban form indicators could contrarily contribute to vitality for different cities, times, or dimensions, suggesting that urban spaces bearing these qualifications might not be constantly attractive. We suggest a consideration of local spatiotemporal characteristics in urban revitalization policies.