Provided are a method and system for realizing a service-based mobile originated short message service. The method for realizing a service-based mobile originated short message service (MO SMS) includes: after receiving a short message transferred from a user equipment, an SMSF entity querying, from a NRF entity, information of a network function that can provide a MO SMS forwarding service; when it is determined, according to a query result, that a corresponding SMS-IWMSC can provide the MO SMS forwarding service, the SMSF entity sending the short message to the SMS-IWMSC; and the SMS-IWMSC sending the short message to a SC, so that the SC sends the short message to a corresponding receiver of the short message.