Climate in Beijing is defined as "continental monsoon." The four seasons are distinctly recognizable. Autumn is the best time to be in Beijing; the temperature is mild and the sun is out a lot. The temperature in spring is nice, too, but it is very dry and winds whip sand around the city.
Summer can be unbearably hot, and winter is equally freezing cold, assisted by winds blowing down directly from siberia. Beijing nice clothes for going out at night, but for touring during the day wear casual clothes and comfortable sturdy shoes.
In autumn, jeans and a sweater are usually enough. In the warmer months, T-shirts and light pants or shorts are the best bet. In the colder months, it is wise to dress in layers; long underwear and jeans, shirt, sweater and down jacket. It you want to go local, you can buy a cool army coat (jun da yi )for less than 100 yuan.