UGUI multiple Image lead to drop frame problem

As shown in Figure 10 Image
One of the first Image (Image set to see the picture) full screen,
Second or so up and down are 10,
Third or so up and down are 20,
and so on…
Tenth or so up and down are 100,
Where FPS is Text display.
1.png in the Image is a 5X5 of the white picture.
But FPS dropped to more than thirty Android on the phone.
(test models: millet Note3, Samsung on5 G5500 Galaxy)72554-image.png

I tested it and find that it’s the Image size which lead to the drop of frame rate. The bigger the image is(not the size of origin texture but the area of image in the canvas), the lower frame rate we have. But I don’t known why this happened.