My leakage circuit breaker trips every 3 hours in rainy days. What happened?

Probably because it is too humid, it leads to excessive leakage current and leads to leakage protection.

Every 3 hours is definitely not absolute, because the household leakage protector does not trip regularly, I suggest you check the line.

You can use the elimination method: first turn off all the switches in the house, and then push them all the way to see which circuit caused the trip;

You can also use DMG2670 digital megohmmeter to test the insulation resistance. If it is a wet circuit, the insulation resistance will be very low, and it can basically be judged that it is a problem caused by the circuit.