I work for SamsungSDS which is the subsidiary company of Samsung group.
-> I work for SamsungSDS which is a subsidiary company of Samsung group.

It is a big-sized company and was founded in 1985

-> Correct sentence!

and has been so far about 30 years
-> and has been about 30 years so far

and there are about 15,000 employees.
-> Correct sentence!

It ranks top in the IT service in the Korean market.
-> Correct sentence!

We mainly support other Samsung subsidary company such as Samsung electronics.
-> We mainly support other Samsung subsidary companies such as Samsung Electronics.

As you know Samsung electronics has been making Galaxy phone and digitalTV.
-> As you know Samsung Electronics has been making Galaxy phones and digital TVs.

My job is SW engineer for digitalTV in there.
-> I am a software engineer for digital TVs in there.

My workplace is the R&D center of samsung electronics in Suwon City.
-> My workplace is located in the R&D Center of Samsung Electronics in Suwon City.

The place is very large and it is only for Samsung company.
-> Correct sentence!

There are three tall buildings of R&D center.
-> There are three tall R&D buildings.

In July, 2 twin buildings were established.
-> Correct sentence!
 
This area has many parks, restaurants, sport center, soccer fields
-> This area has many parks, restaurants, sport centers, soccer fields
 
and many people take a walk after lunch.
-> Correct sentence!

I get to the office at around 9 a.m.
-> I get to the office around 9 a.m.

As soon as I sit on my chair, usually check the urgent e-mails.
-> As soon as I sit on my chair, I usually check my urgent e-mails.
 
After that take a coffee break.
-> After that I take a coffee break.

I'm a general manager
-> Correct sentence!

and manage 60 employees under me.
-> and there are 60 employees under me.

If you come to my office, the first thing you will notice is the digital-TV
-> Correct sentence!

and there are computer, fax machine, printer, projector, stationery and DTV as developing sample.
-> and there is a computer, a fax machine, a printer, a projector, stationeries and DTV as developing samples.

 I really satisfied with what I do and the people I work with. 
-> I'm really satisfied with what I do and the people I work with. 

Hi there!

Thank you for introducing your company through this writing. You must be a lucky guy for working for such a nice and big company in Korea. Have a good night!