Hi Im reading an article from the net where i found this expression so what's mean Google Sandbox?? thinks
sometimes a site starts to do too well in the google results, so google puts it in the sandbox for awhile which means it won't show up very high in the search results while google decides whether it is a good site or just spam usually it happens to new sites that need to prove themselves first, so if you are in the sandbox just ignore it and keep making your site good and improving your content and usually the site just comes out of sandbox after awhile and it is all good
The theory is that Google won't allow a website to rank high in the SERP's for about 1 year because it has to earn trust with Google and establish it's self - this is what is refereed to as the "Google Sandbox".
no sure way to tell if you are in the sandbox, but usually you can see symptoms like if you were ranking higher for a keyword it might suddenly fall way down in rankings, or google might not index as many of your pages