A wireless tire pressure sensing device, a method for setting a standard tire pressure thereof and a wireless tire pressure sensing activation device adjust the tire pressure of each tire in a vehicle to a standard tire pressure according to a requirement of the vehicle after the wireless tire pressure sensing device is mounted in each tire, maintain each tire at the standard tire pressure for a preset time period or employ the wireless tire pressure sensing activation device to transmit a setup instruction to the wireless tire pressure sensing device to set a current tire pressure as the standard tire pressure. The wireless tire pressure sensing device can be set up with the standard tire pressure and conveniently modified. As no threshold value of tire pressure needs to be pre-stored, wireless tire pressure sensing devices with different threshold values are not necessarily prepared beforehand, thereby effectively lowering the stocking pressure on inventory management.