e.g. During the analysis there will be defined the necessity in implementation of specified ..

or: During the analysis there will be performed the analysis of existing indicators ... etc.

Just this will do

During the analysis, the necessity in implementing something will be determined

During the analysis, the existing indicators will be analyzed

I can't vouch for their correctness, but at least they don't baffle the reader all too much.

Hope this version of the sentence will be much clearer in spite of the fact it's too long:

During the analysis, the existing indicators of tax reporting forms provided by the STA regarding the necessity of including each indicator into tax declaration forms or one or more declaration attachments will be analyzed

Sorry, but this is still not a good sentence. It's hard to understand. Here are a few comments.

It's terrible style to say 

'During the analysis  . . . . . .  (things) . . . . . will be analyzed.' 

What does 'indicators of tax reporting forms' mean?

Is there some reason why you have to cram all this into one sentence? Making sentences too long is a common problem English learners have. It usually just leads to errors and lack of clarity.

How about something like this?

The analysis will deal with the existing indicators of tax reporting forms. These appear on forms provided by the STA. The analysis will look at the necessity of including each indicator on tax declaration forms, and consider the alternative of including each indicator on one or more declaration attachments.

I've had to guess at some of your meaning.

Best wishes, Clive