<p>During national Mega Political events, cities often enter an extraordinary state characterized by intensive security deployment and minimal inflow of external visitors, offering a rare quasi-experimental setting isolate the impact of highly centralized security governance on crime. However, research on how such measures affect crime opportunities remains insufficient. Against this backdrop, to quantify the net effect of high-intensity security measures on crime, the Military Parade Celebrating the Founding of the People’s Republic of China in 2009 and 2019 in Beijing were selected as a case study. The results show that high-intensity security measures reduce crime during event periods, with the most significant effects observed for theft. Crime reduction exhibits spatial heterogeneity, as theft declines more sharply in non-security areas, while robbery and assault show no significant spatial variation. Moreover, the effects are short-lived, with theft quickly rebounding to pre-security levels after security measures are lifted, while robbery and assault remain largely unchanged. These findings suggest that extreme security interventions exert selective and short-lived effects, being more effective for opportunity-based crimes than for violence driven. These empirical results extend the applicability of routine activity theory to extreme security contexts.</p>