A system message indication method, comprising: receiving, by a terminal device, notification information sent by a network device, wherein the notification information is used to indicate a value of first information, the first information comprises at least one bit in a first system message, a quantity of bits comprised in the first information is less than a quantity of bits comprised in the first system message, and the notification information is further used to indicate whether second information is changed, and the second information comprises at least one bit that is in the first system message and that is other than the first information; and the method being characterized in that: if it is determined, based on the notification information, that the second information is not changed, reading, by the terminal device, the value of the first information in the notification information, and updating, by the terminal device, a locally stored first system message based on the value of the first information; or if it is determined, based on the notification information, that the second information is changed, receiving, by the terminal device, a changed first system message, and updating, by the terminal device, the locally stored first system message based on the changed first system message. receiving, by a terminal device, notification information sent by a network device, wherein the notification information is used to indicate a value of first information, the first information comprises at least one bit in a first system message, a quantity of bits comprised in the first information is less than a quantity of bits comprised in the first system message, and the notification information is further used to indicate whether second information is changed, and the second information comprises at least one bit that is in the first system message and that is other than the first information; and the method being characterized in that: if it is determined, based on the notification information, that the second information is not changed, reading, by the terminal device, the value of the first information in the notification information, and updating, by the terminal device, a locally stored first system message based on the value of the first information; or if it is determined, based on the notification information, that the second information is changed, receiving, by the terminal device, a changed first system message, and updating, by the terminal device, the locally stored first system message based on the changed first system message. if it is determined, based on the notification information, that the second information is not changed, reading, by the terminal device, the value of the first information in the notification information, and updating, by the terminal device, a locally stored first system message based on the value of the first information; or if it is determined, based on the notification information, that the second information is changed, receiving, by the terminal device, a changed first system message, and updating, by the terminal device, the locally stored first system message based on the changed first system message.