It has great significance to achieve the fast, in-situ measurement of potassium content in soil to the fertilization in farmland and agricultural production management. The spectroscopy emission characteristics of potassium in soil are studied based on laser-induced breakdown spectroscoy techinque with a 1064 nm wavelength NdYAG laser as the excitation source, the echelle spectroscopy with high resolution and wide spectral range as the spectral separation device and the intensified charge coupled device (ICCD) as the spectral detection device. With the spectral line of 769.90 nm as the analytical line, the best detection delay time is 1 μs, gate time is 5.2 μs, and the limit of detection is 0.006858%. The calibration curve of soil samples is obtained. While the relative error between the predicted value and true value is within 5%. 12 different types of soil with different matrix effects are measured. The result shows that, for the actual quantitative measurement of soil samples with different matrix types, they need to be calibrated respectively. The research result provides a reference for the fast, in-situ quantitative measurement of potassium in soil.