On-demand acquisition method and device of SI are provided. The method includes transmitting a random access preamble to a network, and the random access preamble is used at least for requesting the SI, acquiring indication information related to the SI based on a random access response received from the network; and acquiring the SI, based on the indication information, from the network in broadcast or unicast mode, and the indication information is used for indicating time sequence information and a mode of acquiring the SI. Interaction process between the UE and the network may be simplified, which further effectively reduces signaling overhead during the interaction and avoids a waste of resources.