A communication method and apparatus. A terminal device determines channel state information based on S indexes of S vectors. Each of the S vectors is included in a first vector quantization dictionary. The first vector quantization dictionary includes N1 vectors, where N1 and S are both positive integers. The terminal device sends the channel state information to a network device. Because a vector included in the vector quantization dictionary usually has a relatively large dimension, quantizing channel information by using the first vector quantization dictionary is equivalent to performing dimension expansion on the channel information or maintaining a relatively high dimension. High-precision feedback is implemented by using relatively low signaling overheads.