This paper addresses a slot allocation planning problem for an alliance service operated by a liner carrier and its partners. In practice, co-operative carriers share ship’s capacities according to the respective ratio of their contributed ships for the service, but they can trade the surplus or shortage slots. For each participated carrier, this essential decision relies on its appropriate slot allocation planning to match the expected level of carrying demand for various kinds of containers. From a participating carrier’s viewpoint, this research formulates a model to maximize potential profits in a round trip voyage by optimizing slot allocation and contributed ships. We apply our model to assess a short sea alliance service of the studied company and to conduct the post-analysis for some parameters. The solution results can provide a detailed allocation with a higher slot utilization rate. Furthermore, the influences of slot sale price and ship operating cost are also helpful to the studied company.