Hi Jacky chen,
Thank you for your interest in Syncfusion products.
In our XlsIO, we do not have support to copy chart alone from the existing sheet. We have created the sample to copy the chart with the existing data from sheet1 to sheet2 and we have tested the sample with the 8.3.0.21 assemblies in 3.5 .Net Framework. Could you please get the same and let us know if you have any queries.
Sample:
http://help.syncfusion.com/samples/xlsio.Windows/Supports/CopyChart.zipRegards,
Sathish