Yeah,thanks for your reply.
The link in your post I have read, however, I also check out the known DLLs on the current system as the following registry key:
However, I found that gdal_ECW_JP2ECW.dll isn’t in it.
I have installed QGIS 2.14 and 2.18 and I found the OSGeo4W Shell of these two version will invoke the same dll, it means that the error in my post is always be existed.
However,I found my python script doesn’t need this dll file , so then I moved the gdalplugins to another folder(to prevent demand in later processing). In this way ,the error doesn’t pompt up again.
No matter how , thanks for your answer and kindness.