PSR B0540 - 69 has braking index measurement in its persistent state : n = 2.129 \pm 0.012 .
Recently , it is reported to have spin-down state changes : a suddenly 36 \% increase in the spin-down rate .
Combining the persistent state braking index measurement and different spin-down states , PSR B0540 - 69 is more powerful than intermittent pulsars in constraining pulsar spin-down models .
The pulsar wind model is applied to explain the variable timing behavior of PSR B0540 - 69 .
The persistent state braking index of PSR B0540 - 69 is the combined effect of magnetic dipole radiation and particle wind .
The particle density reflects the magnetospheric activity in real-time and may be responsible for the changing spin-down behavior .
Corresponding to the 36 \% increase in the spin-down rate of PSR B0540 - 69 , the relative increase in the particle density is 88 \% in the vacuum gap model .
And the model calculated braking index in the new state is n = 1.79 .
Future braking index observation of PSR B0540 - 69 in the new spin-down state will be very powerful in distinguishing between different pulsar spin-down models and different particle acceleration models in the wind braking scenario .
The variable timing behavior of PSR J1846 - 0258 is also understandable in the pulsar wind model .