To achieve an unmanned rice farm, in this study, a cotransporter system was developed using a tracked rice harvester and transporter for autonomous harvesting, unloading, and transportation. Additionally, two unloading and transportation modes—harvester waiting for unloading (HWU) and transporter following for unloading (TFU)—were proposed, and a harvesting–unloading–transportation (HUT) strategy was defined. By breaking down the main stages of the collaborative operation, designing module-state machines (MSMs), and constructing state-transition chains, a HUT collaborative operation logic framework suitable for the embedded navigation controller was designed using the concept and method of the finite-state machine (FSM). This method addresses the multiple-stage, nonsequential, and complex processes in HUT collaborative operations. Simulations and field-harvesting experiments were performed to evaluate the applicability of this proposed strategy and system. The experimental results showed that the HUT collaborative operation strategy effectively integrated path planning, path-tracking control, inter-vehicle communication, collaborative operation control, and implementation control. The cotransporter system completed the entire process of harvesting, unloading, and transportation. The field-harvesting experiment revealed that a harvest efficiency of 0.42 hm²∙h⁻¹ was achieved. This study can provide insight into collaborative harvesting and solutions for the harvesting process of unmanned farms.