class Model(nn.Module):
 def __init__(self):
  super(Transfer_model, self).__init__()
  self.linear1 = nn.Linear(20, 50)
  self.linear2 = nn.Linear(50, 20)
  self.linear3 = nn.Linear(20, 2)

 def forward(self, x):
 pass

model = Model()
# 这里是一般情况，共享层往往不止一层，所以做一个for循环
for para in model.linear1.parameters():
 para.requires_grad = False
# 假如真的只有一层也可以这样操作：
# model.linear1.weight.requires_grad = False

optimizer = optim.Adam(filter(lambda p: p.requires_grad, model.parameters()), lr=0.1)