Abstract: In order to evaluate the extent of different sample thickness affecting the measurement of ¹³⁷Cs and ²¹⁰Pb in loess soil, a comparison between simulative calculation on detecting efficiency and actual measurements was conducted through using the Laboratory Sourceless Object Calibration Software (LabSOCS). An increase in the sample thickness results in a decline of the detection efficiency on ¹³⁷Cs and ²¹⁰Pb as shown a logarithm function (P<0.001). An increase in the sample thickness from 5 mm to 80 mm results in 68% and 83% reduction of the detection efficiency for ¹³⁷Cs and ²¹⁰Pb, respectively. The specific activities of ¹³⁷Cs and ²¹⁰Pb in samples determined through the LabSOCS do not change evidently with thickness, suggesting that the LabSOCS can eliminate or correct the effect on detection efficiency resulting from changes in sample thickness. The sample thickness, however, has a significant effect on the analysis precision of ¹³⁷Cs compared with a slight effect for ²¹⁰Pb. A 15 mm sample thickness can be considered as a critical thickness for significantly affecting the analysis precision of LabSOCS. This conclusion is of importance in improving the analytical precision of ¹³⁷Cs and ²¹⁰Pb in soil samples.