Embodiments of this application provide slot format configuration method and device. According to the method, a network device determines a slot format index for performing uplink-downlink transmission with a terminal device. The slot format index corresponds to a row in a slot format information table, and each row in the slot format information table includes positions of uplink symbols, positions of downlink symbols, and positions of unknown symbols in a slot. The network device sends the slot format index to the terminal device. The terminal device determines a slot format for the uplink-downlink transmission from the slot format information table based on the slot format index. The uplink-downlink slot configuration method provided in the embodiments of this application may satisfy specific requirements of low-latency and high-reliability communication scenarios.