Hi
It will be cold from Feb to Apr in Beijing as the low temperature can be about -8c, while it will become warm and hot in May and June as the high temperature will be about 33C.

First week of April this year i was in Beijing. The first two nights the temperature is +10c. For the next six nights it was between 0c to +5c. Day temperature not more than +10c. Spring was three weeks late so we end up arriving Beijing at the tail end of winter. In fact TV news broadcast said some parts of China is having snow fall. When we visit Badaling we could see fresh snow along the walls. It was very cold and windy throughout our eight days in Beijing. Better bring along thick jacket, hat to cover your ears, hand gloves and a pair of non-skid shoe(safety shoe) for Badaling. By the way Da Dong Roast Duck Restaurant at Dongsi 10 Tiao is good. Have a pleasant trip.