Mesoscale convective systems (MCSs) are frequent over the U.S. Great Plains during spring. The link between large-scale environments and spring MCS initiation were well established. Here, historical and future changes of spring large-scale environments favorable for MCS initiation are investigated using an MCS tracking dataset, ERA5 reanalysis, and 20 CMIP6 models. The frequency of Great Plains low-level jet (GPLLJ)-related MCS environments is found to have increased by ~41% from 1979 to 2019, consistent with the enhanced GPLLJ and more frequent MCSs. Comparing CMIP6 AMIP and historical experiments, we find that the observed GPLLJ strengthening and more frequent MCS environments are mainly due to the decadal sea-surface temperature variations rather than external forcings. Under a high emission scenario, the frequency of GPLLJ-related environments favorable for MCS initiation will increase by ～65% during 2015-2100, along with a stronger GPLLJ, suggesting more frequent MCSs over the U.S. Great Plains in a warming world.