is it possible to mine a block with hashrate lower then mining pools(or which have very high hashrate with lot of gpu)
if, yes then in what condition it's possible. ?
and anyone mined a block by low hashrate?
Yes it is still possible to mine with low hashrate. It just means that solving the block is slow. This is because a miner has very low chances of solving the block. But if there is an opportunity, they will still try to solve it, that's why they call the network probabilistic.
But you should also be aware of the risk, because of its low hashrate, there are also chances that it won't be able to solve a block.
And when that happens you have no profit of course. So if you really want to earn even if the hashrate is low, you should use efficient miners.