The Jehol and Yanliao biotas of northern China, two world‐class Lagerstätten with abundant biomass and biodiversity, provide critical clues to Mesozoic terrestrial ecosystems. Their evolution is a response to the destruction of the North China craton. However, the impetus for the rapid bloom of the biotas remains a mystery. Mesozoic large‐scale volcanic‐sedimentary strata in northern China are rich in terrestrial organisms. Statistical analyses show that volcanic nutrient element delivery, biomass, and biodiversity in these stratigraphic sequences increase synchronously, while harmful elements have the opposite change with them. These observations reveal the coevolutionary relationship between volcanism and terrestrial biotas. The increased nutrient element supply and inhibited harmful element delivery to terrestrial ecosystems from the voluminous volcanic products, produced under the geodynamic regime of paleo‐Pacific subduction and cratonic destruction, could create a conducive environment for the biodiversity and high prosperity of Mesozoic terrestrial biotas. Plain Language Summary The weathering of volcanic products can quickly provide material supply for ecosystems, including nutrient and harmful elements. The availability of these elements in volcanic‐sedimentary sequences can provide key evidence for the intrinsic relations between volcanism and terrestrial biological evolution. Through statistically‐based big data analyses, we determine the changes in nutrient/harmful element delivery, biomass, and vertebrate and entomic diversity of the Mesozoic fossil‐bearing volcanic‐sedimentary strata in northern China. Excluding the interference of pyroclastic flows on the fossil records, the results reveal the significant contributions of elevated volcanic nutrient supply to the flourishing of the Jehol and Yanliao biotas. Meanwhile, the inhibited release of harmful elements has limited impacts on the biotas. This study opens a new path for multidisciplinary investigations to explore the feedback relationship among regional tectonics, volcanism, and terrestrial biotas. Key Points Mesozoic terrestrial biotas in northern China coevolved with volcanism during the paleo‐Pacific subduction and cratonic destruction The increasing supply of volcanic nutrients promoted the flourishing of the Jehol and Yanliao biotas Inhibited volcanic toxic delivery facilitated the rapid bloom of the terrestrial biotas