The Mid-Brunhes Event (MBE, ~430 ka) marks a pronounced amplification of global glacial-interglacial climate amplitude and a fundamental reorganization of the Earth system. Palaeoclimatic proxies from the Chinese Loess Plateau indicate that Marine Isotope Stage (MIS) 13a, immediately preceding the MBE, was the warmest and wettest interglacial of the Middle–Late Quaternary in East Asia, whereas global marine and other terrestrial archives consistently identify the post-MBE MIS 11c as the humid and thermally optimal interglacial worldwide. To investigate the variability of the East Asian monsoon climate and the response of fluvial-lacustrine sedimentary sequences to East Asian monsoon climate change across the event, we analyzed the mechanisms governing down-core variations in volumetric magnetic susceptibility (κ, 10^-5 SI) preserved in the lacustrine-fluvial-aeolian succession preserved of core 23GL from the Weihe Basin over the past 1.18 Ma. By integrating previously published paleoclimate proxies from the loess-paleosol sequence of the Chinese Loess Plateau, we investigated variations in East Asian Summer Monsoon (EASM) precipitation as recorded by κ during MIS 12~10 and analyzed their orbital periodicities. Results show that the low κ in the shallow-lake setting is related to (i) the low input of coarse debris flux and (ii) possible reductive dissolution of ferrimagnetic minerals during early diagenesis. In the littoral settings, the κ values are systematically higher; exceptional κ peaks coincide with lake-level fall that shifted the depositional site closer to the paleo-shoreline, thereby increasing the flux of ferrimagnetic coarse detritus. In fluvial settings, high-amplitude κ variability is primarily controlled by unstable sedimentary environments and variable oxidation-reduction conditions associated with intermittent subaerial exposure. Within the overlying aeolian sequence, κ clearly defines two intervals: (i) a low-κ interval (~30~12 ka) correlative with the MIS 2 loess sub-layer L1LL1, and (ii) a high-κ paleosol layer S0 (<12 ka) formed during the Holocene. Spectral analysis of the κ series for the 500~320 ka window reveals a statistically significant precession cycle (~20 ka), demonstrating that EASM precipitation is paced by precession-dominated boreal summer insolation. During MIS 12, two pronounced precipitation minima occurred at ~460 ka and ~451 ka across East Asia—expressed in the core as 30- to 50-cm-thick sand beds that coincide with high κ and mean-grain-size values. The transition from shallow-lake to littoral-lake and finally to fluvial settings across the MBE is attributed to the combined effects of (i) the reduced EASM precipitation from late MIS 12 to MIS 9, (ii) the longer glacial stages after the MBE, and (iii) the enhanced evaporation during the extended MIS 11c interglacial.