Regarding the transformation of the urban green space pattern, this study analyzed the mutual conversion between urban green space types in Beijing through the transposition matrix of urban green space types. The increase in green area was mainly from cultivated land from 2000 to 2005. A total of 219.63 km
2 of cultivated land was converted into forest land and grassland, accounting for 76.58% and 47.30% of the converted areas of forest land and grassland, respectively, which were concentrated in the north, east, and south of the urban-rural transition zone. At the same time, 60.82 km
2 of green space was transferred out, mainly for construction land, scattered in the entire urban-rural transition zone. On the whole, the policy of returning farmland to forest and grassland implemented by Beijing in 2002 has achieved remarkable results. The area of urban green space transferred from 2005 to 2010 was lower than that transferred during 2000-2005. Construction land was the main source of the increase in the green area. The transferred area is 70.27 km
2, mainly in the inner area of the central city. Compared with 2000-2005, the transferred area of green space has increased significantly. The total transferred area is 460.23 km
2, of which 51.31% was converted to construction land and 29.50% was converted to cultivated land. Forest land is the main type of green space transfer, and it is mainly converted into construction land and cultivated land. The transfer areas are 119.30 km
2 and 106.18 km
2, respectively, and they are concentrated in the urban-rural transition zone and the new urban area. From 2010 to 2015, the transferred-in area of urban green space increased. The total transferred-in area of green space is 260.45 km
2, mainly from construction land and cultivated land, which accounted for 45.03% and 38.63% of the total transferred-in area of green space, respectively. Among the two, the cultivated land is mainly converted to forest land, and most of the construction land is converted to grassland. At the same time, some of the green space was transferred out, mainly to construction land, and accounting for 66.67% of the total green space transferred out. Among the contributing types, the areas of forest land and grassland converted to construction land are 46.36 km
2 and 34.62 km
2, respectively. Spatially, the transformation of each category is mainly distributed in the northern, eastern and southern parts of the urban-rural transition zone and the new urban area. From 2015 to 2020, the transferred-in area of urban green space has increased significantly, and the total transferred-in area of green space reached 698.55 km
2. This was mainly from construction land and cultivated land, which accounted for 47.94% and 30.22% of the total area of green space transferred. Among these two, the total areas of converted forest land and grassland are 469.81 km
2 and 228.74 km
2, respectively. At the same time, the transfer area of urban green space has also increased to 310.88 km
2. Construction land is the main type of green space transfer. The areas of forest land and grassland converted to construction land are 72.58 km
2 and 62.02 km
2, respectively, accounting for 54.51% and 34.86% of the total forest land and grassland transfer areas. The transformations of the different regions are mainly distributed in the urban-rural transition zone and the new urban area (
Fig. 4).