Is there any sia hardfork happening on January 31st 2018?
Is this true ?

can someone explain in more detail .
There is a hardfork planned at block number 139000, approximately by the end of January. It is aimed to correct the mining Difficulty Adjustment Algorithm.
Take in mind this is a non-contentious fork: all the community, mining pools and infrastructure is accepting it. At such, there will not be a "split" in two coins, no airdrop. The old blockchain will be abandoned.