I found that cause conflict with some plugin name “Redux Framework”
when i disable this plugin , i can make new blog . but this plugin is main request theme plugin. When disable many theme function is disappear.
500 Internal Error is a generic error and says about some issue on the server and can be caused by different things. Anyway, to understand its nature you need to see your server error logs or enable PHP error display on the website. If you can’t do this, you need to contact your hosting provider for help in this question. Here is an article that may help you understand the error better http://www.wpbeginner.com/wp-tutorials/how-to-fix-the-internal-server-error-in-wordpress/