A data connection establishment method and a terminal device, where the method includes receiving, by an application processor (AP), a switch-on instruction, sending, by the AP, a network searching instruction to a communications processor (CP), where the network searching instruction instructs the CP to search for a network, receiving, by the AP, subscriber identity module (SIM) card status change information and network status change information from the CP, and sending, by the AP, a data connection establishment instruction to the CP based on the SIM card status change information and the network status change information, where the data connection establishment instruction instructs the CP to establish a data connection to the found network.