how to evaluate the quality of scientific journal? Hope that the question is not a duplicate, I could not find anything similar. 

I am doing a PhD in mathematical economics but I usually look at math journals and I am trying to adapt some technical methods from there to economics when it is necessary. 

What I am always curious about, as I am not familiar at all with mathematics journals, I don't know which journal is a good quality journal in mathematics (as there exists a huge bunch of journal in mathematics, if I am not wrong)  I don't know if the paper published in the journal is a really credible reference.

Besides Google Scholar citations, what are the best ways to understand if a journal (in the field of mathematics or other) is a well ranked journal ?
There is no straight answer, since as Tom commented, "good quality" can have several meanings. Further, a journal can be considered good for a specific domain and not for another.

What I usually do:


Check the impact factor (and compare it with "known good" journals),
see some of the published works (Usually to discard automatically accepted stuff that has horrible english and worse results...)
Talk to other people with more experience. In your case, what do you advisor thinks? Or any other professors that usually publish in that area?


Another interesting concept is if the journal is correct for your work. 

Nature is an awesome journal, but I caters to specific domains and requires a very high quality article. Sometimes it makes more sense to send the work to a "less good" journal that is specific to your domain and which "matches" the level of your work. As long as there is a proper review involved, it works. 

(For instance, sometimes you don't have time to further develop something, or there is not much more to be done/improved, etc... instead of "losing" the work, you publish it in a "reputable", "less good" venue)

The ability to match  work &lt;-> journal is important and comes from experience. If you don't have it yet, ask for the help of someone who does. That's why advisors are there! :)