If you cancel after 24 hours, you will need to pay a certain fee, which will be deducted from the price.
China Airlines Cancellation Policy, says If you suffer from a medical condition or the death of a family member, you can claim a full refund or reschedule your flight at no additional cost.
A non-refundable flight will receive a travel credit that you can use to purchase future flights.
If Air China cancels the flight, in that case they will reschedule the flight or provide a full refund at source.
If you have purchased an Air China flight ticket with a travel agency, you can contact the agency to cancel your flight.
Cancellation fees may apply in most cases, but if cancellation is made within the specified time period, no cancellation fee needs to be paid. As mentioned above, no passenger will be required to pay an China Cancellation Fee if the reservation is canceled within 24 hours of purchase. The airline also gives the option of canceling to all passengers before 72 hours after the flight takes off.

Another thing travelers need to remember is that there should be a week (seven days) left before the flight takes off, otherwise the 24-hour rule does not apply. Even if canceled within the initial 24 hours, the cancellation is applicable if the flight is less than one week before take-off.