Since dist is the same for each loop iteration, and you are only updating model, you should return a handle to the line object before you start looping and just update the YData property. Similarly, you should just do the same for the text object.
y1 = Mean(1);
x1 = Mean_step(1);
y2 = max_cap./10;
x2 = 0;
b = y2;
aaa = (x1*y1)+(y1)*(x2*y2-x1*y1)/(y1-y2);
bbb = (x2*y2-x1*y1)/(y1-y2);
dist = 0:1/3:1600;
model = aaa./(dist + bbb);
hp = plot(dist, model, 'r-', 'Linewidth', 1.5);
txt1 = ['Y = ' num2str(aaa) ' / (X + (' num2str(bbb) '))'];
ht = text(580, 700, txt1, 'FontSize', 8);
for k = 2:length(Mean_step)
y1=Mean(k);
x1=Mean_step(k);
aaa=(x1*y1)+(y1)*(x2*y2-x1*y1)/(y1-y2);
bbb=(x2*y2-x1*y1)/(y1-y2);
model = aaa./(dist + bbb);
hp.YData = model;
txt1 = ['Y = ' num2str(aaa) ' / (X + (' num2str(bbb) '))'];
ht.String = txt1;
drawnow()
end
