Data pixel value

how to check image pixel value in SNAP Sentinel 1 software

Dear Zhuhaxixiong

Did you mean the Pixel info toolbar, If I understand your question?..

maybe ?where is the tool?

You can activate pixel info from the view menu in SNAP toolbars (Tool Windows) and Pixel info.
then click on the image that will show the pixel info x, y with lat. / long. position.