Hi @azhangbojun,
Have you tried using a virtual environment instead of miniconda, as suggested in this post: Error in Installing Keras on RStudio Cloud ?
I believe the important pieces are:
library(reticulate)
library(keras)
virtualenv_create("myenv")
install_keras(method="virtualenv", envname="myenv")
Please let me know if this helps or not!
-Joshua C. Forest