Live crabs can be preserved for a longer period of time by the following methods:

1. Prepare a plastic bucket, put the live crabs into the bucket, add the right amount of water, and pay attention to the water not to be too deep, so as not to crush the crabs.

2. Place the bucket in a cool and ventilated place, avoiding direct sunlight and high temperature.

3. Check the water in the bucket every day, keep the water clean and replace the water in the bucket.

4. If you need to keep it for a long time, you can put the crabs in the freezer of the refrigerator, keep the temperature between 5-10 degrees Celsius and check the condition of the crabs regularly.

In short, preserving live crabs requires keeping the water clean, avoiding high temperature and direct sunlight, as well as checking the condition of the crabs regularly and disposing of dead crabs in time.