2. Usually, crabs of normal size need to be boiled for 30 minutes. After the water is boiled, put the crab in the water and cook it. When the crab is very big, it needs to be steamed for a long time, but try to control it within one hour. Otherwise, the time is really too long, which will affect the taste of crabs and affect eating. You can turn the crab belly up before steaming to prevent the crab roe from showing.