Recent years have seen a rapid growth of location-aware applications such as targeted marketing, restricted content delivery and location-based security check. Although existing delay-based IP geolocation techniques work well in some developed countries, the assumption of a strong delay-distance correlation that they often rely on may fail in many developing countries for poor network connectivity. To obtain more accurate delay-based IP geolocation results in poor-connected networks, an IP geolocation method based on rich-connected sub-networks is presented in this paper. At first, the network connectivity of one particular network is measured. Next, if the network is poor-connected, the method will divide it and search rich-connected sub-networks based on properties such as ISP and location information of probing hosts and landmarks. Then, based on the discovered rich-connected sub-networks, landmarks and probing hosts are deployed and selected to measure data such as delay, distance and topology, etc. At last, the location of the target host is estimated by modifying the processes of existing delay-based IP geolocation techniques based on selected landmarks and probing hosts. The experiments which cover 30 provinces and 3 major ISPs of China show that the proposed method can find corresponding rich-connected sub-networks and significantly improve the performance of existing typical delay-based IP geolocation techniques in an actual poor-connected network.