I have a young brother who is very nice and kind and prays and fasts. I discovered recently that he browses pornography sites, bad pictures of women. I don't know how to face him and discuss it with him in convincing way. Please reply from Islamic point view and his health .

Praise be to Allah, the Lord of the Worlds; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

The best way to advise your brother is by hiding from him the fact that you know what he was doing especially since he is a man who prays and fasts. So, if you unveil to him his secret this might have a very negative effect. In fact, the person whose wrong doings are not known to others is more prone to change his behaviour than the one whose bad behaviour is already uncovered. Know also that his prayer will hold him back from continuing to commit sins. Ahmad reported from Abu Huraira that a man came to the Prophet and said: "A given man (he did not name him) prays at night then during daytime he steals". The Prophet said: "What he says (in his prayer) will stop him (from stealing)". So, the Prophet did not ask the man to give him the name of that person who steals to inflict the retribution of stealing on him; he (the Prophet) left the matter veiled because the bad that man did will be purified by the prayer.
Now, what you should do is to say in front of him, among other things that looking at the Awrah of women is forbidden and that Allah rewards those who leave something bad for His Sake. Ahmad reported from Qatada that he said that the Prophet said: "You never leave something because of your fear of Allah except Allah will give you something better". Try to take any opportunity to remind him of the good and the bad.
Invoke Allah while prostrating in your prayer to make him leave this bad habit. If you can occupy him with something other than the Internet do so.
Allah knows best.