Abstract: The K-feldspar rocks, mechanically activated by a microcrystalline mill with different times, were used to study effects of microcrystalline grinding on size distribution, potassium releases and bioavailability. The results showed that the cumulative percentage of fine particles (d10 m) in Kfeldspar rocks which treated with 10 min, 40 min, 120 min and 180 min respectively reached 51.69%，65.44%，85.34% and 93.93%. With increasing ground time，the specific surface area obviously increased, the diffraction peak decreased remarkably and the potassium release amount improved significantly. Among them, the T3 treatment activated as 180 min had the best effect of potassium release amount with 6118.8 mg/kg and 2867.8 mg/kg by 2 mol/L HNO3 and distilled water respectively. The total potassium of samples treated as 10 min, 40 min, 120 min and 180 min with acid treatments was 2.46, 1.81, 2.19 and 2.13 times higher than that of the distilled water treatments. The total potassium extracted by two solutions was 0.50%-5.73% in K-feldspar and the form was still mainly mineral potassium, but the microcrystalline K-feldspar rock with higher bioavailability could promote growth of gain amaranth and K accumulation.