As a special product of the evolution of urban-rural regional systems, rural hollowing has become a major constraint to China’s rural revitalization. This paper attempts to construct a theoretical framework of rural multidimensional hollowing from the perspective of population outflow, and to comprehensively assess the level of rural hollowing from the dimensions of population, economy and land. Based on this, this paper describes in detail the characteristics and facts of population outflow and rural hollowing in Longxi County, which is located in Longzhong Loess Hilly Regin. The key factors of rural hollowing are identified in terms of individual characteristics, geographic environment and socio-economic attributes. The main conclusions are as follows: (1) Longxi County has significant spatial differences in population outflow. The proportion of floating population in the household population is as high as 28.6%. The villages with intra-provincial preferences show a “center-periphery” circle distribution pattern, and villages with extra-provincial preferences are mainly located in the boundary area. The rural hollowing level of Longxi is characterized by “economic hollowing (Eh) > population hollowing (Ph) > land hollowing (Lh)”. The hollowing level of each dimension has different spatial distribution characteristics, and the rural hollowing (Rh) level shows a spatial pattern of “high in the east and low in the west, high in the south and low in the north”. (3) The influencing factors of rural hollowing vary significantly and are greatly influenced by the geographical and socio-economic attributes of the villages. When one factor (economic or geographical environment) is dominant, low-intensity intra-provincial mobility may occur. However, when all factors are combined, a high-intensity, multi-directional flow trend emerges within and outside the province. This study contributes theoretical insights into understanding the social changes in rural areas during the rapid urbanization process where population outflows occur, and can also provide inspiration for addressing issues in rural transformation.