A method for paging a terminal device across heterogeneous networks, where networks using different wireless standards send paging messages and location management information, and thus the load terminal devices can be alleviated and wireless resources occupied can be reduced. The method includes: selecting, by a current network, another network to execute a paging procedure, when receiving user data and determining a corresponding communication interface of the terminal device in the current network to be in a Dormant Mode, where the another network uses wireless standards different from the current network; sending, by the another network, a paging message to the terminal device to enable the terminal device to reconnect to the current network. A terminal device and network system is also provided.