Abstract: Laser induced breakdown spectroscopy (LIBS) has been used to analyze the concentration of potassium in compound fertilizer. Self-absorption was prone to appear in the formation process of plasma because of the high-content potassium in samples. The atomic spectral line 404.40 nm of potassium was determined as the optimized line by analyzing the excitation energy, transition probability and self-absorption of spectral lines. Experimental stability with different average numbers of pulses was discussed, and the results indicated that the average measurement of 100 pulses had a lower relative standard deviation. Nine samples were analyzed and seven of them were tested to establish the calibration curve of measured concentration of K2O. The linear fitting degree of the calibration curve was 0.989 and the measured concentration of K2O in the other two samples was well consistent with the corresponding reference concentration with an absolute error of less than 0.3%.