There is only one metro at shenzhen railway station.
1. please get off at Laojie Station and then follow the English signs to Dongmen street
2. please get off at Huaqiangbei station
3. at Shenzhen Railway Station, you could take a train to get to Guangzhou quickly.

Of course, at the wholesale markets around Guangzhou Railway Station, such as White Horse Wholesale Market, you could find more.

Thanks Mr. Leo for your prompt answer.

I am still looking for the best hotel to stay (which is near to the wholesale market). Pls advise which one is better, Hotel Elan or Liuhua Hotel? And how far is this hotel to Beijing pedestrian street? Do i have to use bus/train?

You can take the subway line one at the place which you stay in and off at Laojie station to get to the Dongmen.
You have to take the subway line one and off at Huaqianglu to get to the Huaqiangbei to buy the electronics.
Please take the train at Luohu to get to Guangzhou; there are few railway stations in Guangzhou, its better for you to off at the Guangzhou railway station (general) to by the clothes. It takes about 70 minutes to get to the Guangzhou railway station (general) from Shenzhen and it costs you 75RMB.
There are many wholesales markets for clothes in Guangzhou and in some other cities such as Foshan ,Huizhou ,Dongguan and Meizhou.
If you need a help ,I think I can help you with the information.

Good luck!

Hi Mr Alimuslim, really appreciate for ur kind help. Few more inguiry:-

1) Pls suggest me the best hotel to stay (still unsure either to choose Hotel Elan or Liuhua Hotel or u have any better choice?), I want the hotel near to the wholesale market and railway station.
2) Apart from the wholesale market, is there any other places i should go? i read that Beijing Predestrian Street is a "must go" place. How to get there?
3) By looking at ur name, i believe you are a Muslim right? (correct me if im wrong). Then, can u suggest me any halal restaurant in Guangzhou?

1) I suggest you to stay in Liuhua hotel or some other hotels near the railway station; it might be much more convenient to go to the wholesales markets around the city.
2)it is good to visit the much more wholesales markets, especially the places such as Foshan Dongguan Huizhou Meizhou,Humen,Shayong ;as you know ,most of the factories or some wholesales markets are located in the suburbs ,the rate of shops are much cheaper there, so the price of the products are still cheaper than downtown of Guangzhou ;you can take the subway line 2 at the railway station or some other places and off at the Gongyuanqian station.
3)Yes, I am Muslim, elhemdulilah; there are so much Halal foods all over the city, the restaurant named Baghu-Bostan at the Zhanqianlu is much convenient to you if you stay in a hotel around the railway station; there are some good restaurants in Xiaobeilu running by some Muslims such as Turk, Arabian, Uyghur ,Hui Muslim, Indian African Muslims.
Good luck and have fun!