The invention belongs to the technical field of potassium-containing rock treatment, and particularly relates to a method for extracting potassium in potassium-containing rock. The method includes thefollowing steps that first, primary calcination is conducted; second, cooling is performed, and the primarily-calcined product is cooled to be at an indoor temperature; third, an ultrasonic reactionis carried out, the cooled product is mixed with an acid solution, the mixture is put in an ultrasonic reaction still, the material temperature is controlled to be 80-100 DEG C for reacting, and solid-liquid separation is conducted after reacting to obtain solids; fourth, a microwave reaction is carried out, the ultrasonic reaction product is mixed with auxiliaries to be put into a microwave reaction still, and the material temperature is controlled to be 120-130 DEG C for reacting; and fifth, secondary calcination is conducted. By adoption of the method, the advantages of increasing the dissolution rate of potassium and improving the activity of the potassium are achieved, various kinds of potassium-containing rock can be treated at the same time, sewage discharge are heat exhaustion arereduced, and treatment time is shortened.