Abstract: Abstract: Over the last three decades, paddy fields on the Sanjiang Plain have experienced rapid expansion. It has an important impact on regional food security, ecological environment and socio-economic development. Fujin is a typical area of Sanjiang Plain, with both common agricultural area and reclamation area, and the land use pattern is the epitome of Sanjiang Plain. In our study, used 1 000 m×1 000 m grid cell to scientifically analyze the spatial-temporal variation and driving factors of paddy fields, in Fujin from 1989 to 2002 and from 2002 to 2015. And elevation, slope, soil type, distance to railway, distance to river, distance to town and policy factors were selected as driving factors in this paper. With the help of GeoDetector, we analyzed the role of these seven factors in paddy field change and their relationship. The results indicated that such paddy fields have increased by approximately 349 900 hm2 from 1989 to 2015, and the paddy field process of reclamation area was earlier than that of common agricultural area. In the early 1990s, in order to adjust the agricultural planting structure, the local government began to encourage farmers to plant paddy rice in large areas. During this period, paddy rice planting area increased rapidly. From 1989 to 2002, the areas with the high proportion of paddy field expansion were mainly located in the reclamation areas in the northeast and southeast of Fujin County, and some other agricultural areas. From 2002 to 2015, the project of cultivated land development and improvement was implemented, and the cultivated land in Fujin reached a high level of agricultural development, and all the conditional areas were basically converted to paddy fields. The areas with higher proportion of paddy field expansion were mainly located in the southwestern common agricultural area and the northern reclamation area of Fujin City. In addition, the main driving factors of paddy field expansion in 1989-2002 were policy factors and soil types. The interaction between these factors was mostly enhanced by two factors. It showed that in the 1990s, under the guidance of the policy of agricultural structure adjustment, Fujin took the lead in reforming the soil types suitable for paddy fields and the land with superior location conditions. As a result, a large number of cultivated land resources with superior development conditions in the eastern reclamation area of Fujin were reclaimed into paddy fields. From 2002 to 2015, the influence of natural factors on paddy field change becomes weaker. The main driving factors of paddy field expansion are the distance from rivers to railways, and the interaction among these factors is mostly non-linear. Natural factors are no longer the key to restrict the development of paddy fields. Driven by market interests, dryland that meets the conditions of paddy field transformation is converted to paddy fields. The spatial difference of paddy field change in Sanjiang Plain is the result of the interaction of various driving factors. The driving factors and their relationships are different in different periods. Geographic detectors can make a more comprehensive analysis of various influencing factors. The results can provide theoretical basis for the protection of cultivated land and the rational utilization of cultivated land resources in Sanjiang Plain.