If you owe the Government tax, you will be charged interest if you don't file your tax return by April 30. However, if the Government owes you a refund, there is no penalty if you file your tax return after April 30. You can also file your tax return by sending it to the Canadian Embassy or consulates in China, but then by doing that you are telling the Government that you are not in Canada, and you probably don't want to do that.