For each training image, I want to randomly crop four 224*224*3 patches and together with their mirrored ones compose a 8 * 224 * 224 * 3 minibatch. Certainly, the mask is processed in the same way. 
I implement a class dataset, and I concat 8 patches in it's function '__getitem__' and return it. In the dataloader, I get the tensor [ 1 * 8 * 224 * 224 * 3], so i need to Squeeze it. But after that, I find that all the patches are changed which are not fliped.  Meanwhile, I find that the RandomCrop is not a 'Really Random'.

This is my code.

class dataset(data.Dataset):
    def __init__(self, img_path, mask_path):
        self.img_path = img_path
        self.mask_path = mask_path

    def transform(self, image, mask):
        image_res, mask_res = [], []
        for i in range(1):
            i, j, h, w = transforms.RandomCrop.get_params(
                image, output_size=(224, 224)
            )
            print(i, j, h, w)
            image = tvf.crop(image, i, j, h, w)
            mask = tvf.crop(mask, i, j, h, w)

            image_flip = tvf.hflip(image)
            #image.show()
            #image_flip.show()

            mask_flip = tvf.hflip(mask)

            image_res.append(np.array(image))
            image_res.append(np.array(image_flip))
            mask_res.append(np.array(mask))
            mask_res.append(np.array(mask_flip))
        return np.array(image_res), np.array(mask_res)

    def __getitem__(self, item):
        image = Image.open(self.img_path)
        mask = Image.open(self.mask_path)
        print(image.size, mask.size)
        image_res, mask_res = self.transform(image, mask)

        for i in range(image_res.shape[0]):
            img = Image.fromarray(image_res[i])
            #img.show()
        #totensor = transforms.ToTensor()
        #image_res = totensor(image_res)
        #mask_res = totensor(mask_res)
        return torch.tensor(image_res), torch.tensor(mask_res)
    def __len__(self):
        return 1

for i, (x, y) in enumerate(dataloader):
    print(x.size(), y.size(), '--')

    img = Image.fromarray(x[0, 0].numpy())
    # print(type(img))
    img.show()
    img = Image.fromarray(x[0, 1].numpy())
    # print(type(img))
    img.show()

    x = torch.randn(1, 2, 2, 2)
    print(x[0])

    x = torch.squeeze(x, dim=0)
    y = torch.squeeze(y, dim=0)
    print(x)

    for j in range(x.size()[0]):
        tx = x[i]
        ty = y[i]
        img = Image.fromarray(tx.numpy())
        #print(type(img))
        #img.show()