i will go to shenzhen/guangzhou on 24-28 october 2015, please advise me on the weather that time

Well, according to the weather data, the temperature of these two places of that period of time is 68 °F to 86 °F.
It's warm and comfortable. T-shirts and light jackets are enough for you to prepare.

If it was anything like this year then it will be really comfortable. Not too humid but still warm. I went to the beach on November 2nd and 17th this year in SZ and was not cold! Bring a cardigan or maybe even a light jacket and long trousers as the evenings are colder, however, it is still comfortable to sit out all night and one rarely gets to cold.

Hope this helps.