An input/output (I/O) interface-based signal output method and apparatus. The method includes determining whether a voltage output by a core power supply domain of a first chip is lower than a preset threshold voltage of the first chip, and when the voltage output by the core power supply domain is lower than the threshold voltage, generating a first level signal according to a control function of the first chip over a second chip, where the first level signal is used to enable the second chip to be in an ignoring state after the second chip receives the first level signal, and sending the first level signal to the second chip through an I/O interface, where the ignoring state indicates that the second chip ignores a control signal and a data signal that are sent by the first chip where the method improves stable performance of a chip product.