Is there a bus connecting the old Huaihua train station to the South Train Station?

Yes, you can take public bus no.19 to the South Railway Station directly. The ticket fare is CNY 2 per person. If you wanna take a cab directly, the cab fare is around CNY 20.

Is there any bus about the return way?

When you get out of the South Railway Station, you can walk 190 meters westwards and turn right for 180 meters to Gaoyan Road. Then you may go across the road to Gaotie South Bus Stop. Afterwards, you can take bus no.116 back to the old Railway Station directly.

From the old Railway Station to the South Railway Station, you may need to walk about 320 meters southwards to West Yingfeng Road and turn left for about 140 meters to Huairong Hotel Bus Stop. Then you can take bus no.12 to the South Railway Station directly.