HYOC implemented twice large-scale capacity expansion of optical fiber lines of 4^th ring of Beijing from year 2013. The project in 2013 was to install 5 microducts of 10/8mm size into preexisting 40/33mm silicon ducts, and then 96 cores air blown microcables were blown into microducts. The project in 2014 was to install 1 microduct of 14/12mm and 2 microducts of 12/10mm, and then 288 cores and 216 cores of microcalbes were blown into one 14/12mm and one 12/10mm microduct, and the third one was preserved for future use. The utility of pre-existing ducts were improved by 3-5 times after the capacity expansion. The projects were first successful case of capacity expansion by microcables in China, and also a millstone of HYOC’s history.