A transmission method of system information, a user equipment, a network side device, a system and a storage medium are provided. The method includes: receiving, by the UE, system information sent by a network side device, the system information is part of system information of the network side device; sending, by the UE, a request message to the network side device, wherein the request message is used to request the system information required by the UE; receiving by the UE, the system information required by the UE in on-demand system information sent by the network side device, wherein the on-demand system information is another part of system information of the network side device other than the part of system information of the network side device.