i am at down town in beijing how can i reach to world park down town

Since I am not very clear about where you are, so it is hard to tell in detail.
Generally speaking, the local subway line 9 can take you to reach Guogongzhuang Station where you can change to Fangshan Line to reach Dabaotai Station.
Get out of the station from Exit A or B, you can see the park easily.