The invention discloses a quick determination method for security boundary quantity of a power distribution network. The quick determination method comprises the following steps of selecting observation feeder lines, and judging a contact relation thereof; finding an extra element of each loop of observation feeder line; and determining the boundary quantity by selecting a corresponding inclined/linear boundary quantity calculation formula according to the contact relation of the feeder lines. By further researching of the generation mechanisms of the security boundary of the power distribution network, the security boundary quantity determination method according to the contact relation of the feeder lines in the power distribution network is provided; the method does not need security domain simulation or listing writing of a security boundary equation; and instead, the security boundary quantity can be quickly determined by observing the network structure of the power distribution network and by combination with the boundary quantity calculation formula.