The chain-type variant rotorcraft exhibits excellent maneuverability in constrained environments. However， its flight attitude control becomes challenging and unstable when operating under variable loads. To address this issue， this paper proposes an attitude control method based on active disturbance rejection control （ADRC） for the rotorcraft under variable load conditions. Firstly， a dynamic model of the variant rotorcraft is established with a focus on variable load scenarios， and the impact of load changes on attitude control is analyzed. Secondly， the coupling between states， load variations， and internal and external disturbances are collectively treated as a total disturbance， which is estimated and compensated using an extended state observer （ESO）. Finally， flight experiments are conducted to verify the stability of the attitude control for typical configurations， as well as the feasibility of attitude control under both gradual and sudden load changes. The performance of PID and ADRC controllers is compared in terms of adaptability to variable load conditions， and the impact of configuration transitions on attitude disturbance is further analyzed. The results show that the maximum attitude tracking error in each axis does not exceed 8°， and the maximum response delay is within 0.3 s. The proposed ADRC-based control method demonstrates excellent stability and robustness， providing a solid technical foundation for the load-carrying operations of variant rotorcraft.