The potassium ion in the drilling fluid aims to stabilize shale and restrain the clay’s dilatability. So, the potassium ion content must be measured accurately so as to control the performances of drilling fluid. SY-2 hand operated centrifuge is used to measure the potassium ion content in the drilling fluid whose potassium ion content is more than 5000mg/l or KCl concentration is bigger than 3.5lb/bbl. Use the perchloride to deposit the potassium ion in the centrifuge, then determine the volume of the deposit, and numerate the content from the criterion curve.