This application provides a data transmission method and an apparatus, applied to an intelligent vehicle, and a connected vehicle, to select an appropriate protection policy for to-be-transmitted data, and balance calculation resources of ECUs. The method includes: A first ECU obtains to-be-sent data. The first ECU determines a protection policy corresponding to the to-be-sent data from a plurality of protection policies, where the plurality of protection policies include a plurality of different encapsulation manners for the to-be-sent data, and the plurality of protection policies include at least two protection policies with different calculation amounts for processing the to-be-sent data. The first ECU encapsulates the to-be-sent data according to the protection policy corresponding to the to-be-sent data, to obtain an encapsulated packet. The first ECU sends the encapsulated packet to a second ECU, where the first ECU and the second ECU are any two ECUs in a vehicle.