原帖：http://www.matlabsky.com/thread-11209-1-1.html

文件交流上好像有画3y轴的函数：

function [ax,hlines] = plotyyy(x1,y1,x2,y2,x3,y3,ylabels)

%PLOTYYY - Extends plotyy to include a third y-axis

%Syntax:  [ax,hlines] = plotyyy(x1,y1,x2,y2,x3,y3,ylabels)

%Inputs: x1,y1 are the xdata and ydata for the first axes' line

%        x2,y2 are the xdata and ydata for the second axes' line

%        x3,y3 are the xdata and ydata for the third axes' line

%        ylabels is a 3x1 cell array containing the ylabel strings

%Outputs: ax -     3x1 double array containing the axes' handles

%         hlines - 3x1 double array containing the lines' handles

%Author: Denis Gilbert, Ph.D., physical oceanography

%Maurice Lamontagne Institute

�pt. of Fisheries and Oceans Canada

%email:   

%Web: http://www.qc.dfo-mpo.gc.ca/iml/

%April 2000; Last revision: 14-Nov-2001

if nargin==6

   ylabels{1}=' '; ylabels{2}=' '; ylabels{3}=' ';

elseif nargin > 7

   error('Too many input arguments')

elseif nargin < 6

   error('Not enough input arguments')

end

figure('units','normalized',...
       'DefaultAxesXMinorTick','on','DefaultAxesYminorTick','on'); 

[ax,hlines(1),hlines(2)] = plotyy(x1,y1,x2,y2);

cfig = get(gcf,'color');

pos = [0.1  0.1  0.7  0.8];

offset = pos(3)/5.5;

pos(3) = pos(3) - offset/2;

set(ax,'position',pos);  

pos3=[pos(1) pos(2) pos(3)+offset pos(4)];

limx1=get(ax(1),'xlim');

limx3=[limx1(1)   limx1(1) + 1.2*(limx1(2)-limx1(1))];

ax(3)=axes('Position',pos3,'box','off',...
   'Color','none','XColor','k','YColor','r',...   
   'xtick',[],'xlim',limx3,'yaxislocation','right');

hlines(3) = line(x3,y3,'Color','r','Parent',ax(3));

limy3=get(ax(3),'YLim');

line([limx1(2) limx3(2)],[limy3(1) limy3(1)],...
   'Color',cfig,'Parent',ax(3),'Clipping','off');

axes(ax(2))

set(get(ax(1),'ylabel'),'string',ylabels{1})

set(get(ax(2),'ylabel'),'string',ylabels{2})

set(get(ax(3),'ylabel'),'string',ylabels{3})

% 例子
% x = [0 0.1 0.2 0.3 0.4 0.426 0.5 0.6 0.688 0.7 0.8 0.9 1.0];
% y = [268.95 272.36 275.07 277.07 277.93 278 276.5 267.16 248.2 244.3 200.37 137.71 58.7];
% a = [0 0.225 0.408 0.566 0.693 0.718 0.776 0.82 0.831 0.831 0.818 0.784 0.6];
% k = [2.55 2.254 2.063 1.886 1.733 1.687 1.552 1.368 1.207 1.187 1.023 0.873 0.6];
% ylabels{1}='轴1';
% ylabels{2}='轴2';
% ylabels{3}='轴3';
% [ax,hlines] = plotyyy(x,y,x,a,x,k,ylabels);
% legend(hlines, 'y = x','a =x','k = x',2)