The invention relates to the field of plant irrigation, and provides a plant irrigation method and device. According to the method, whether cumulative water consumption reaches a preset first threshold value or not is judged by calculating the cumulative water consumption of plants; if the cumulative water consumption reaches the preset first threshold value, automatic irrigation of the plants is performed. Therefore, the irrigation can be performed without depending on a temperature sensor and the skill level of a maintenance worker, and the irrigation can be directly performed according to cumulative water consumption of a plant wall; meanwhile, the cumulative water consumption of the plants represents current water consumption and former water consumption, so that dynamic water consumption updating can be realized in real time, and weather changes can be adapted. Therefore, the irrigation effect is greatly improved.