Abstract: The concentration of ⁴⁰K in seawater was measured directly by HPGe γ spectrometer. Based on the LabSOCS software, the maximum detection efficiency corresponding to the optimal geometric shape and parameters was calculated, as a result, the analysis of the concentration of ⁴⁰K in seawater can be finished in 3 hours with relative standard deviation less than 10% for sample net count. Compared with other methods, γ-spectrum analysis has few influencing factors, and it does not need any pretreatment process which is very convenient. Therefore, the γ-spectrum analysis is worth promoting as an alternative method in environmental radiological baseline study.