The present disclosure provides an uplink grant-free transmission method in Ultra Reliable & Low Latency Communication (URLLC), a terminal side device and a network side device. The uplink grant-free transmission method includes: receiving a configuration parameter, the configuration parameter including first information indicating a correspondence between time-domain resources for URLLC uplink transmission and identifiers of Hybrid Automatic Repeat reQuest (HARQ) processes; and after the arrival of a URLLC service, transmitting data for the URLLC service using a corresponding HARQ process on an available time-domain resource for the URLLC uplink transmission.