Background: In the era of a pandemic like COVID-19, monitoring the sentimental changes of the population is an urgent need, especially for the policy makers of the public health. A possible solution is to build a fast and low-cost surveillance system by using the sentiment analysis of Twitter data. Unfortunately, choosing a suitable sentiment classification model is still challenging. The general pre-trained model may be insensitive to the new specific terms of the pandemic. The early-trained model may have a bias issue due to the incomplete specific corpus. Although it is reasonable to assume the late-trained model is relatively reliable, it is usually available months after a pandemic begins. Methods: This paper conducts the sentiment analysis of Twitter data and compares different models. Furthermore, we propose a strategy for using the pre-trained, early-trained, and latetrained models in a surveillance system based on Twitter data. The first two models can be used together in the early stage, while the last model can be used in the late stage. This study also analyzes the relationship between the sentimental changes of COVID-19-related Twitter data and the public health policies and events. Results: Our results indicate that applying the pre-trained model to preprocessing early training samples may improve the early-trained model. Both models can work together by making up each other in the surveillance system in the early stage. Conclusions: A fast and low-cost surveillance system is critical to the policy makers of the public health in a pandemic. This work uses the sentiment analysis of Twitter data to evaluate people’s attitudes to public health policies and events. We propose a strategy to make the surveillance system effective since the early stage. This study also connects the sentimental changes of COVID19-related Twitter data to the public health policies and events.