Thanks for reply. I’ve run your code, however, nothing improved. I listed the outputs as follows.
Output for the initial training without loading any pre-trained model:
    [Errno 2] No such file or directory: 'NGramModel.tar'
    Epoch [1/10], Loss: 6.3162, ACC: 0.1006
    Epoch [2/10], Loss: 6.1846, ACC: 0.1345
    Epoch [3/10], Loss: 5.7875, ACC: 0.1446
    Epoch [4/10], Loss: 5.1115, ACC: 0.1661
    Epoch [5/10], Loss: 4.1613, ACC: 0.1921
    Epoch [6/10], Loss: 3.1089, ACC: 0.2576
    Epoch [7/10], Loss: 2.1107, ACC: 0.3153
    Epoch [8/10], Loss: 1.2641, ACC: 0.3887
    Epoch [9/10], Loss: 0.7448, ACC: 0.5062
    Epoch [10/10], Loss: 0.5428, ACC: 0.5977

Output for the second training with loading the model yielded by the initial training:
    model loaded successfully
    Epoch [1/10], Loss: 4.3901, ACC: 0.0723
    Epoch [2/10], Loss: 2.7416, ACC: 0.1706
    Epoch [3/10], Loss: 1.5863, ACC: 0.2633
    Epoch [4/10], Loss: 0.8832, ACC: 0.3514
    Epoch [5/10], Loss: 0.6362, ACC: 0.4621
    Epoch [6/10], Loss: 0.5090, ACC: 0.5672
    Epoch [7/10], Loss: 0.4624, ACC: 0.6328
    Epoch [8/10], Loss: 0.2824, ACC: 0.6881
    Epoch [9/10], Loss: 0.2198, ACC: 0.7130
    Epoch [10/10], Loss: 0.1668, ACC: 0.7164