Yiwu Airport. Many cities fly to Yiwu: HK, Seoul, Beijng , Guangzhou, Shenzhen, Shantou... Although many flights can easily delay, flying to Yiwu is still a good option if you can.
Hangzhou Airport. Hangzhou Xiaoshan Airport (HGH), is only 1.5 hrs away from Yiwu. Many taxi, buses(coaches) are going from Hangzhou airport to Yiwu daily. Hangzhou has more flights and cheaper rates. Here is more info: travel from Hangzhou airport to Yiwu.
Shanghai Pudong airport (PVG) is 4 hrs from Yiwu. Taxi/car is recommended. Fast train from Shanghai to Yiwu only takes 1.5-2.0 hrs. But it can easily take 5+ hrs before you check in Yiwu hotel. Here is more info: travel from Shanghai to Yiwu.