[Objective] In the past 30 years (1988-2017), rice planting patterns, potassium (K) fertilization application and crop yield all changed greatly in the rice-cropping areas of China. Therefore, it is necessary to follow spatio-temporal changes in readily available K in paddy soils in those regions, which may help provide guidance to improvement of soil K utilization efficiency use and rationalization of K fertilizer application.[Methods] Based on the data gathered from the nationwide paddy soil monitoring network, laid out in 1988~2017, spatio-temporal variation of soil readily available K, K fertilizer partial factor productivity (PFP-K) and K apparent balance (KAB) was analyzed in Northeast China, the Yangtze River Delta, Middle Reaches of the Yangtze River, South China and Southwest China, and relationships between the three also discussed.[Results] In the past 30 years, soil available K content was significantly higher Northeast China than in the other four regions. In the Middle Reaches of the Yangtze River, soil readily available K increased first and then levelled off in content, but in in the Northeast China, the Yangtze River Delta and South China soil readily available K content were steady first and then increased in content with the experiment going on, while in Southwest China little change was observed. Soil readily available K content was significantly and positively related to PFP-K. In Northeast China, the Yangtze River Delta, the Middle Reaches of the Yangtze River and South China, for the increase of each 10 mg·kg-1 of soil readily available K in paddy soil, PFP-K increased by 0.31, 1.51, 0.26 and 0.49 kg·kg^-1, respectively. The paddy soils in China and all the five regions exhibited a declining trend or remained in balance in KAB during the period from 1988 to 1998, but a rising trend was observed during the period from 1998 to 2017. South China was the highest in KAB of paddy soil, followed by the Middle Reaches of the Yangtze River, Northeast China, the Yangtze River Delta and Southwest China in a decreasing order. The relationships between KAB and soil readily available K content (P<0.05) in paddy soils of the country and in the five regions could be fitted with a linear equation.[Conclusion] Therefore, for the paddy soils in China, soil readily available K content was on a rising trend during the period from 1988 to 2017, but soil readily available K content and its annual growth rate varied quite sharply from region to region. Higher soil readily available K content could significantly promote rise of PFP-K, and the K apparent surplus in paddy soils as a result of long-term rice cultivation was conducive further to increase in soil readily available K content.