Thank you for your kind answer.
It works!
For convenient reference for others, I post my concrete code here.
self.fc6_to_conv = nn.Conv2d(512, 4096, kernel_size = 7, stride = 1, padding = 0)
self.fc6_to_conv.weight.data = vgg16.fc6.weight.data.view(self.fc6_to_conv.weight.size())