diff --git a/gmtsph-global.sh b/gmtsph-global.sh
index 1b37a66..406ba6c 100755
--- a/gmtsph-global.sh
+++ b/gmtsph-global.sh
@@ -23,7 +23,7 @@ For futher explanations, please look for GMT's manuscripts.\nAuthor: Yi Zhang (z
 			printf "%s\t%s\n" "-i" "input grid file"
 			printf "%s\t%s\n" "-r" "data range. The template will ditect the input data range automaticly, the use of this option will overwrite the range."
 			printf "%s\t%s\n" "-l" "central longitude value of the plot, the default value is 0"
-			printf "%s\t%s\n" "-u" "data unit. The default is meter."
+			printf "%s\t%s\n" "-u" "data unit. The default is meter. use 'km+Uk' to append '+Uk' option to the psscale command"
 			printf "%s\t%s\n" "-c" "color cpt. The default is rainbow."
 			printf "%s\t%s\n" "-a" "axis labels. The deafults are x (m) and y (m)."
 			printf "%s\t%s\n" "-g" "use grdgradient. The default is false."
@@ -85,7 +85,7 @@ else
 	fi
 	#-C${cptfile}+Uk 使用km（色标单位除1000
 	#如果unit等于km则在cptfile后面添加+Uk
-	if [[ ${unit} == 'km' ]]; then
+	if [[ ${unit} == 'km+Uk' ]]; then
 		gmt psscale -Dx0.5i/-0.3i+w2i/0.07i+h -C${cptfile}+Uk -Bxa -By+l${unit} -O >> $psfile
 	else
 		gmt psscale -Dx0.5i/-0.3i+w2i/0.07i+h -C${cptfile} -Bxa -By+l${unit} -O >> $psfile