I. Introduction
In recent years, deep learning has attracted great attention from industry and academia, and has been greatly developed in the medical, financial, education, Internet, and etc [1]–[3]. The performance of the deep neural network model is closely related to the scale and quality of the data [4]. More high-quality data can greatly improve the performance of the model. In reality, data is often held by different organizations. For example, for diabetic retinopathy, different hospitals can collect case samples of different characteristics (such as region and age). If these samples are put together, the accuracy and robustness of the detection model can be significantly improved. However, privacy and data laws in some countries or organizations prohibit transmission of raw data across country or organization [5], [6]. In view of the current situation that data in various professional fields is not open, how to make full use of richer data features under the premise of ensuring data privacy of different organizations has become an urgent challenge for deep learning.