Abstract: In the era of big data, stream processing has been widely applied in financial industry, advertising, Internet of things, social networks and many other fields. In streaming scenarios, the generation speed of stream data tends to be fluctuant and difficult to predict. If the streaming peak is larger than system capacity, the system may run slowly or even crash, which leads to job failure. If excessive resources are provided in case of streaming peak, there can be unnecessary waste under light load. In order to solve the matching problem between stream processing load and resources, stream processing system should be elastically scalable, which means that provided resources can be adjusted automatically according to the real-time change of stream flow. Although some researches have made great progress in stream processing, it is still an open problem that how to design an elastic scalable system. This paper introduces eSault, an elastically scalable stream processing framework based on Actor model. eSault firstly manages the processing units stratified hierarchically based on Actor model, and realizes scalability with two-layer routing mechanism. On this basis, eSault proposes an overload judgment algorithm based on data processing delay and light load judgment algorithm based on the data processing speed to efficiently allocate the resources, and achieve elastically scalable stream processing. Experiments show that eSault has good performance, and can achieve flexible scalability well.