thank you for your response.
I'm using our own board, not official development kit, and Quartus 15.
The fitter error messages are:
Error (176310): Can't place multiple pins assigned to pin location Pin_G1 (IOPAD_X10_Y17_N14)
Info (176311): Pin x1 is assigned to pin location Pin_G1 (IOPAD_X10_Y17_N14)
Info (176311): Pin altera_reserved_tms is assigned to pin location Pin_G1 (IOPAD_X10_Y17_N14)
Error (176310): Can't place multiple pins assigned to pin location Pin_G2 (IOPAD_X10_Y17_N21)
Info (176311): Pin x2 is assigned to pin location Pin_G2 (IOPAD_X10_Y17_N21)
Info (176311): Pin altera_reserved_tck is assigned to pin location Pin_G2 (IOPAD_X10_Y17_N21)
Error (176310): Can't place multiple pins assigned to pin location Pin_F5 (IOPAD_X10_Y16_N14)
Info (176311): Pin x3 is assigned to pin location Pin_F5 (IOPAD_X10_Y16_N14)
Info (176311): Pin altera_reserved_tdi is assigned to pin location Pin_F5 (IOPAD_X10_Y16_N14)
Error (176310): Can't place multiple pins assigned to pin location Pin_F6 (IOPAD_X10_Y16_N21)
Info (176311): Pin x4 is assigned to pin location Pin_F6 (IOPAD_X10_Y16_N21)
Info (176311): Pin altera_reserved_tdo is assigned to pin location Pin_F6 (IOPAD_X10_Y16_N21)
In my design, signal x1,x2,x3,x4 are single-endded ios.
If I removed the nios system .qsys file from my project, fitter didn't report any error.
In the max10 configuratin manual, it says "any JTAG-related IP cannot be used if you enable the JTAG pin sharing feature in your design".
So I believe the NIOS .qsys file must has JTAG-related IP in it.
Chao