If fire need oxygen, then why does it go out when you blow on it?

Burning needs all the three conditions, namely fuel, heat (high temperature) and oxygen. They are known as a "fire triangle". When you blow hardly on a small fire, too much heat is removed and the temperature is lowered too much. As a result, the fire goes out.

Also needs heat. If you blow too hard you cool it down below the flame point and increase the level of CO2.
Light breathes will increase the burning rate.

IF you check out a black smiths forge you will see that regulated air blowing into the fire increases the combustion.

the main reason is that when you add oxygen by blowing, you push away the fuel. It is not usually a case of removing heat, but instead is one of removing fuel (the fire is happening to gas molecules, not solids or liquids, so you can blow away the gaseous fuel). Many things require heat to re-add gaseous fuel, so if you kill the burn by flushing away fuel, the fuel source (like wood, say) can lose the heat it needs to replace the fuel you just blew away. Usually, you end up with a sooty or smoky smoulder when that is what has happened (like after you blow out a candle). Smoke and soot are not gas forms of fuel, the fuel sources are still dumping fuel into the air but it isn't turning into gas, and they have to be in gas form for the reaction to happen. Sometimes, the fire can reignite after the fuel content gets high enough even if the fire was totally out for a bit.

This is why blowing on hot coals in a wood fire can cause the fire to start up again, instead of going out. Blowing on those coals causes them to heat up and give off more gaseous fuel, and of course you are also introducing some oxygen. Plenty of heat, just looking for a good fuel to air mixture for burning.

How big a fire can you blow out? A match perhaps? In any fire the vapour of the fuel is what is burning and a small fire can be extinguished if you can cool the fuel sufficiently to stop it producing enough vapour to fuel the fire. For larger fires you need water to cool the fuel sufficiently.

Matches and candles, yes, fires? not so much.

maybe your blow is filled with Nitrogen

Try blowing oxygen on the fire and see what happens DjD. ;-( Be careful though.

There’s too much oxygen dumbaass

Forces

Because we breathe in more oxygen than we breather out.

We're breathing out CO2.

you are blowing carbon dioxide actually...only inhale is O2.

because you breathe out CO2 but blow out Air = Oxygen

We breath out carbon dioxide... https://www.google.com/search?q=what+gas+do+we+breathe+out&rlz=1C1GCEB_enGB835GB835&oq=what+gas+do+we+bre&aqs=chrome.0.0j69i57j0l4.4344j0j7&sourceid=chrome&ie=UTF-8