The soil potassium supplying characteristics of 5 representative paddy soil samples from Guangdong Province were studied by simulation experiment and pot experiments under exhaustive cropping with rice. The results showed as following:(1)There have better correlation between the effective potassium extracted by 2 mol/L HNO_3 and the amount K uptake by rice than by other methods. It is suggested that the available K extracted by 2 mol/L HNO_3 was a suitable index for evaluating the K supplying capacity. (2) The amount of 1 mol/L HNO_3-extractable K was unsuitable to evaluate soils exhausted as it was higher than that pre-exhausting and had no correlation or negative correlation with the amount K uptake by rice.(3) The K supplying capacity of five different soils were followed the order: soil derived from Pearl River Delta deposits>soil derived from granite>soil derived from sandstone>soil derived from limestone>soil derived from basalt.