Abstract: Lightning electromagnetic pulses pose a significant threat to sensitive electrical and electronic devices. The enhancement effect of urban tall structures on lightning electromagnetic radiation fields has become a prominent research topic. As one of China’s most lightning-active regions, Guangdong-Hong Kong-Macao Greater Bay Area features 600-m Canton Tower, the tallest structure. In 2024, direct measurements of current peaks are conducted on 492-m height of Canton Tower, encompassing 11 first return strokes of downward flashes, 23 subsequent return strokes of downward flashes, and 60 subsequent return strokes of upward flashes. These are compared with corresponding current peaks estimated by the Guangdong-Hong Kong-Macao Lightning Location System (GHMLLS). Additionally, numerical simulations of radiation fields of the first and subsequent strokes to Canton Tower are conducted to analyze differences in Canton Tower’s enhancement effects on radiation fields of different lightning return stroke types. Results show that the arithmetic mean (median) of ratios of GHMLLS-estimated current peaks to directly measured current peaks are 2.1 (2.1) for downward first strokes, 2.8 (2.8) for downward subsequent strokes, and 2.8 (2.8) for upward subsequent strokes. Canton Tower’s enhancement effect on electromagnetic radiation fields of the first strokes is significantly weaker than that on subsequent strokes. For the first strokes of Canton Tower, the ratio of GHMLLS-estimated to directly measured current peaks shows a negative correlation with peak current magnitude, while subsequent strokes exhibit a positive correlation. Simulation results indicate that when the exponential decay constant of the current in the return stroke channel is constant, longer upward connecting leader (UCL) reduces the enhancement effect of Canton Tower on the electromagnetic radiation field of the first stroke. When UCL exceeds 100 m, Canton Tower’s enhancement on first-stroke radiation fields is significantly lower than that on subsequent strokes with only 5-m UCL. Since UCLs before Canton Tower’s first strokes often exceed several hundred meters,far longer than those before subsequent strokes,this is likely the key cause for the weaker enhancement effect on first strokes.