is there any bus from xinnanmen bus station to huanglong?

No, there is no direct bus from that bus station to Huanglong. If you also plan to visit Jiuzhai Valley, you can take a bus from Xinnanmen Bus Station. After a visit, you can also take a bus to HL then. BTW, only two buses are in service in the morning, at 06:30 and 07:00.

Or you can go to the Chadianzi Bus Station, where you can take a bus to Songpan first. (The buses are available at 06:30, 08:30 and 11:30). In songpan, I hear there are three buses to Huanglong at 06:00, 07:00 and 14:00. If you fail to catch that bus, just hire a car, the fare would be CNY200 around.