There's no international flight into yiwu directly. Depending on which port you enter China, you will have some options.
Shanghai to Yiwu: If you fly to Shanghai first, you can take a bus or train to yiwu and it's about 4-5 hours.
Guangzhou to Yiwu (Canton to Yiwu) If you fly to Guangzhou, you can take a connection flight to yiwu airport. That's the ideal travel plan, esp. for those who attend the Canton Fair in October.
Yiwu Fair is from 22nd to 26th of October each year, designed to be held right during the break of Canton Fair so international visitors can attend both. In case you miss the flight from Guangzhou to yiwu, you can take the flight to Hangzhou, and take bus to yiwu from Hangzhou, it's about 1-2 hours.
Trains from SHANGHAI to YIWU
Train takes about 5 hours or less from shanghai to yiwu. There're plenty of options between shanghai and yiwu. Make sure you board a quicker and clearner one. The staff at your hotel should provide you with booking assistance.

Rain No.	From	To	Dep. (SHANGHAI)	Arr. (YIWU)	Travel Time	Air-conditioned
1527	Shanghai	Huaihua	15:00	20:12	0d05h12m	Yes
1597	Shanghai	Hengyang	14:56	19:50	0d04h54m	Yes
2135	Shanghai	Nanchang	17:05	22:19	0d05h14m	Yes
2311/2314	Shanghai	Jiujiang	14:19	18:53	0d04h34m	No
5085	Shanghai	Jiangshan	22:12	03:39	0d05h27m	No
K11/K14	Shanghai	Hankou	16:43	21:12	0d04h29m	Yes
K111	Shanghai	Guiyang	09:06	13:32	0d04h26m	Yes
K123/K122	Shanghai	Wuchang	14:06	18:07	0d04h01m	Yes
K149	Shanghai	Zhanjiang	12:21	16:43	0d04h22m	Yes
K163	Shanghai	Fuzhou	16:23	21:00	0d04h37m	Yes
K181	Shanghai	Kunming	16:53	21:19	0d04h26m	Yes
K197/K200	Shanghai	Xiamen	08:40	13:31	0d04h51m	Yes
K253/K252	Shanghai	Yichang	16:15	20:25	0d04h10m	Yes
K351/K354	Shanghai	Chengdu	15:38	20:04	0d04h26m	Yes
K71/K74	Shanghai	Chongqing	19:58	00:05	0d04h07m	Yes
K79	Shanghai	Kunming	15:30	19:38	0d04h08m	Yes
K809	Shanghai	Lanxi	07:21	11:47	0d04h26m	Yes
N509	Shanghai	Lanxi	07:19	11:54	0d04h35m	Yes

Bus From Shanghai to Yiwu
If you take bus, it leaves about every 1 hour and available at various long distane inter-province bus stations ( called chang tu ke yun zhan in Chinese) . Some stations got more schedules than others. Make sure you know which station you are going to. Again, the hotel staff should be able to give you directions. You may want to go to either the general station ( or Ke yun Zong zhan at No. 1662 of Zhongxing Road) or Pacific Station (tai ping yang station at No. 710 Hengfeng Road.) Actually buses are just fine if you don't get car sick.
Private transportation From Shanghai to Yiwu (Recommended for group of 2 people or more)
If you want more comfort and privacy, we can also arrange private car/van pick up from Shanghai to Yiwu. It costs about 1000-1200 RMB regularly, but with our long business relationship with many taxi companies and private drivers, your discount rate is only 800-850 RMB. It's actually quite economical too, if you come in group of 2 people or more.