An assistance data transmission method, comprising: obtaining, by a network device, assistance data from a positioning data center in a segmentation manner, wherein the assistance data is segmented based on a transport block size of a system information block, SIB, that is supported by the network device, and assistance data comprises system message period indication information, which indicates a system message transmission period to be used by the network device; and sending, by the network device, the assistance data to a terminal device in a broadcast manner, wherein the assistance data is data used by the terminal device to perform positioning, wherein the obtaining, by a network device, assistance data from a positioning data center in a segmentation manner further comprises: obtaining, by the network device, a packet sequence number of each piece of segmented assistance data, and indication information, from the positioning data center, wherein the indication information is used to indicate whether a packet is a last packet, wherein the obtaining, by a network device, assistance data from a positioning data center in a segmentation manner further comprises: obtaining, by the network device, assistance data of different positioning precision from the positioning data center; or obtaining, by the network device, assistance data specific to different positioning methods from the positioning data center; or obtaining, by the network device, assistance data specific to different satellite positioning systems from the positioning data center. obtaining, by a network device, assistance data from a positioning data center in a segmentation manner, wherein the assistance data is segmented based on a transport block size of a system information block, SIB, that is supported by the network device, and assistance data comprises system message period indication information, which indicates a system message transmission period to be used by the network device; and sending, by the network device, the assistance data to a terminal device in a broadcast manner, wherein the assistance data is data used by the terminal device to perform positioning, wherein the obtaining, by a network device, assistance data from a positioning data center in a segmentation manner further comprises: obtaining, by the network device, a packet sequence number of each piece of segmented assistance data, and indication information, from the positioning data center, wherein the indication information is used to indicate whether a packet is a last packet, wherein the obtaining, by a network device, assistance data from a positioning data center in a segmentation manner further comprises: obtaining, by the network device, assistance data of different positioning precision from the positioning data center; or obtaining, by the network device, assistance data specific to different positioning methods from the positioning data center; or obtaining, by the network device, assistance data specific to different satellite positioning systems from the positioning data center. obtaining, by the network device, a packet sequence number of each piece of segmented assistance data, and indication information, from the positioning data center, wherein the indication information is used to indicate whether a packet is a last packet, wherein the obtaining, by a network device, assistance data from a positioning data center in a segmentation manner further comprises: obtaining, by the network device, assistance data of different positioning precision from the positioning data center; or obtaining, by the network device, assistance data specific to different positioning methods from the positioning data center; or obtaining, by the network device, assistance data specific to different satellite positioning systems from the positioning data center. obtaining, by the network device, assistance data of different positioning precision from the positioning data center; or obtaining, by the network device, assistance data specific to different positioning methods from the positioning data center; or obtaining, by the network device, assistance data specific to different satellite positioning systems from the positioning data center.