The invention discloses an ash conveying system and method for a wastewater spray evaporator. Ash sampling ports are formed in the side surface of an evaporator, the side surface of an ash bucket andthe side surface of an ash storage box. A flue gas outlet pipeline is communicated with a flue gas outlet in the side surface of the evaporator. An outlet in the bottom of the evaporator communicateswith an inlet in the top of the ash bucket. An outlet in the bottom of the ash hopper communicates with an inlet in the top of the ash storage box. An outlet in the bottom of the ash storage box communicates with an inlet of the ash silo through a first valve. An outlet in the side face of the ash storage box communicates with an inlet of an ash mill. An outlet of the ash mill is communicated withan inlet of the ash silo. A plurality of temperature sensors are arranged on the side wall of the evaporator, the side wall of the ash bucket and the central position of the ash bucket, wherein the output end of each temperature sensor is connected with the input end of the controller. The output end of the controller is connected with the control end of the first valve and the control end of theash mill. The system and the method can ensure the normal operation of the evaporator, and can effectively solve the problem that the ash hopper is blocked and scaled.