I am not sure I understand what you mean. Subplot sounds like the solution for this problem. If by a single graph you mean you only want one axes, then the solution that comes to mind is to offset your data and plot it. Assuming all have common x values, and four different y's (column vectors):
off_x = max(x) - min(x);
off_y = max([max(y1)-min(y1), max(y2)-min(y2), max(y3)-min(y3), max(y4)-min(y4)]);
plot(x,y1); hold on;
plot(x+off_x,y2);
plot(x+off_x,y3+off_y);
plot(x,y4+off_y);
Note that you would need to play with the tick labels for them to make sense. Also, if what you want to avoid spaces between the subplots, you could create custom axes, e.g.:
h1 = axes('Position',[0.1 0.1 0.4 0.4]);
h2 = axes('Position',[0.1 0.5 0.4 0.4]);
h3 = axes('Position',[0.5 0.5 0.4 0.4]);
h4 = axes('Position',[0.5 0.1 0.4 0.4]);
