画布太小导致的，你把画布拖动，尽量大一些就会画出来，我用你的程序一开始也是这样，调整下就好了！

是这样的，多谢！另外我想了解一下，如果画布太小，图形在RStudio里面不能自动按比例缩小吗？

你可以看下这个链接，希望对你有帮助！
http://blog.sina.com.cn/s/blog_670445240101lc39.html

The message means that the margins in the figure are too large and do not leave enough space for the plot.
Try reducing the margin.Note you will need to consider what is an appropriate margin setting for each of your different panels, and fine-tune label sizes and so on.

For a totally blank panel, you might as well kill the margin completely:

op <- par(mar = rep(0, 4))
plot.new()
par(op)

实在感谢您！