Surface soil samples were collected at the top and bottom of the Dashiwei karst tiankeng (large karst sinkholes) and measured for the presence of polynuclear aromatic hydrocarbons (PAHs). Comparisons were made on the distribution of PAHs at the top and bottom of the sinkhole, and their probable sources were inferred. The average sum of the 16 U.S. Environmental Protection Agency (USEPA) PAHs measured was 74.48 ng/g. At the top, the sum of PAHs (PAHs) ranged from 23.43 to 88.94 ng/g, with an average concentration of 57.76 ng/g, and at the bottom, they ranged from 43.51 to 190.47 ng/g, with an average concentration of 87.88 ng/g. Among the 16 USEPA PAHs detected, phenanthrene had the highest concentration, with an average soil concentration of 16.11 ng/g, and the lowest PAH, with an average soil concentration of 0.55 ng/g, was dibenzo[a,h]anthracene. Results suggest that the higher concentrations at the bottom were caused by lower sunlight penetration and evaporation. The probable source of most of the PAHs detected was inferred to be from petrogenic sources based on ratios of low molecular weight to heavy molecular weight (LMW/HMW), anthracene to anthracene + phenanthrene (AN/AN+PH), benzo[a]anthracene to chrysene (BaA/CH), and other petrogenic source ratio indicators.