How does urbanisation affect the evolution of territorial space composite function?

Under the background of drastic global changes and the widespread urbanisation process, the problems of urban -rural imbalance, food security and ecosystem degradation arising from land use changes have attracted wide-spread attention. By constructing an analysis framework for the driving mechanism of the territorial spatial composite function, taking 199 county-level units in the Beijing-Tianjin-Hebei region as samples, based on panel data, the influence mechanism of population-land urbanisation on the territorial spatial functions evolution was discussed by using the spatio-temporal interactive fixed effects model and spatial econometric models. It was found that land urbanisation did not contribute as significantly as population urbanisation to the composite level of territorial spatial functions, and this difference stemmed from the substitution effect between population urbanisation and land urbanisation. Population-land urbanisation had a complementary effect on urban space development and a substitution effect on agricultural production and ecological maintenance. And urban space development did not offset the weakening effect on agricultural production and ecological maintenance func-tions. The agglomeration of population to cities and towns and rural construction could alleviate the negative effects of the urban construction space expansion, which was conducive to the sustainable development of territorial space. Therefore, it makes up for the shortcomings of existing research on the evolution mechanism of territorial spatial composite function, and has reference significance for the improvement of territorial space development mode and the optimization of territorial space planning system in urban agglomeration areas.