Abstract: The wood anatomy and systematics study of petrified woods from the Lower Cretaceous Shahai Formation in northern Liaoning show that the petrified woods are all silicified secondary xylem of conifer gymnosperms, belonging to the taxonomic groups of Protocupressinoxylon, Protopiceoxylon and Xenoxylon respectively. The growth rings of novel materials of the current petrified woods are clear, with the early wood to late wood ratio of 0.84-64, and the annual average sensitivity of 0.23-0.3, indicating that the climate has obvious seasonal variation. The trees have a short late-wood growth time and long early-wood time span, that is, the tracheid division is strong in the growing season, and the suitable time for factors such as moisture, temperature, humidity and light last longer. The uneven width of continuous growth rings and existence of false rings reflect that the climate changed frequently at that time, and the average annual precipitation may have a great difference. It can be inferred from the growth characteristics that the Shahai Formation in northern Liaoning was generally humid during the sedimentary period, but there might be some arid-semiarid climate fluctuations. The special anatomical structures in petrified woods such as false ring, traumatic resin canal, twisted growth ring and insect hole reveal that there may be drought, wind disaster and insect pests in the then eco-environment, which are unfavorable for the growth of trees in a short time.