The problem is caused by the command “set format ‘%h’”, which does not exist in Gnuplot 4.6 but does in version 5.0. This problem arose after the release of Gnuplot 5.0. So the solution is either removing the set format ‘%h’ to make draw compatible with older versions of Gnuplot or updating to Gunplot 5.0. I choose the latter one. The flair can work to draw a beautiful graph. I don’t know if anyone else will have the same problem. I use Centos 7.