Does it okay to travel to beijing during winter season?
Yes, you need to post in the Beijing forum rather than the Janda Baik one.
But since I was there in winter last year, the pro and cons are this:
Pro: low season, so accommodation is cheaper, less crowds at the main attractions such as the Forbidden City, Great Wall, etc. Great to experience 0 degree temperature especially for us from tropical climes.
Cons: It is smog season in the north of china. If you think the haze in Malaysia is bad, its much worse there. However it is not necessarily every day, you can still get some clear sky days if the wind blows in thw right direction. If you don't have winter clothing, you need to invest in some before you go.
Enjoy your trip!