I have 40.000+ links in my sitemap and google have indexed like 10.000 of tham. It will be good if i split the sitemap like 10.000 link per sitemap?
There is no option like splitting the xml sitemap file with respect to google , instead you can separate in to two domains if you really want to index all your pages .
The maximum number of links in a sitemap is 50,000 URLs according to Google guidelines. So for now it is okay but you should consider splitting them into sitemap.xml, sitemap2.xml in the future when the number of URLs increase further.
Google will not index all the URLs in the file in one go. To save bandwidth you should split the file up into multiple sitemap files. I would use use at max 5,000 URLs per sitemap to keep the numbers lower. Create a master sitemap that has references to the additonal sitemap files that you have on the site. You can also split up the sitemap based on the structure of the site.
yes, you can create more than one site maps and if you still have more URls just go to google webmaster tool and submit your all URLs. it will index very fast.
i dont know whether there is an option of splitting sitemaps or not, but you can have around 50-60k links in one sitemap, also you can remove old links or irrelevant links from your sitemap, i haven't heard about having multiple sitemaps in one site yet.