This article investigates the time-varying output group formation tracking control (GFTC) problem for heterogeneous multi-agent systems (HMASs) under switching topologies. The objective is to design a distributed control strategy that enables the outputs of the followers to form the desired sub-formations and track the outputs of the leader in each subgroup. Firstly, novel distributed observers are developed to estimate the states of the leaders under switching topologies. Then, GFTC protocols are designed based on the proposed observers. It is shown that with the distributed protocol, the GFTC problem for HMASs under switching topologies is solved if the average dwell time associated with the switching topologies is larger than a fixed threshold. Finally, an example is provided to illustrate the effectiveness of the proposed control strategy.