I loaded an image and I want it to rotate around its center, while its scale is getting larger. I know how to rotate an image around its center originally, but it\'s hard for me
You need to re-set the image's centre after it is scaled (& rotated) as both of these can change the image size.
# rotate and zoom the sprite
self.image = pygame.transform.rotozoom(self.original_image, self.angle, self.scale)
# reset it back to original centre
self.rect = self.image.get_rect(center=self.rect.center)
Another thing to consider is to ensure your image-content is centred within itself. (Imagine a rectangle with only content drawn to one-side) the rotation will be centred geometrically, but still look weird visually as it rotates.