Abstract: In this paper, the Permian-Triassic boundary (PTB) sections of Jiangyou, Gunchaipo, Guangyuan Yangjawan and Shangsi in northern Sichuan are selected for the INAA (instrumental neutron activation analysis) analysis of the REE geochemistry of claystone samples. Through a comparative study of the REE abundances, chondrite-normalized distribution pattern and characteristic parameters of claystone samples from three PTB sections, the paper explores the relationship between REE geochemistry and sudden environmental change at the PTB. The results demonstrate that the δEu, δCe, ΣLREE/ΣHREE-ΣREE, Eu/ΣREE-ΣL/ΣH and chondrite-normalized REE distribution patterns and La–Th–Sc ternary discrimination diagrams for claystone at the three sections all reflect the occurrence of the boundary event and the relationship between the REE geochemistry and sudden environmental change. In addition, through a comparative study of the REE geochemistry of the three PTB sections and standard section, the authors think that the environment during the period of the PTB event was affected not only by intermediate-acid volcanism but also possibly by (alkaline) basic-ultrabasic rocks or ejectas of volcanoes or an extraterrestrial planet. The research results provide new evidence for the study of the catastrophic event of this important geological period in the element geochemical context.