The invention discloses a method for determining the theoretical water irrigation quantity of flue-cured tobacco irrigation and a tobacco field irrigation guide device. Aiming at different flue-cured tobacco growth periods and soil texture types, the soil moisture can be determined in sites, in addition, the current specific retention and the required irrigation quantity are calculated, the guided water irrigation quantity is calculated by combining the forecasted recent rainfall condition, and the suggested water irrigation quantity can also be calculated according to the irrigation mode. The tobacco field irrigation guide device comprises a soil moisture sensor (1), a data collector (2), a portable intelligent terminal (3), a data collecting communication program module (25) and an irrigation guide program module (31), wherein the soil moisture sensor (1), the data collector (2) and the portable intelligent terminal (3) are sequentially connected, and the irrigation guide program module (31) calculates the theoretical water irrigation quantity by a calculating method disclosed by the invention. The method for determining the theoretical water irrigation quantity of flue-cured tobacco irrigation and the tobacco field irrigation guide device have the characteristics that the method is scientific, the results are quantitative, the structure is simple, the carrying is convenient, and the like. The method and the tobacco field irrigation guide device are suitable for being used by wide tobacco growers and technical personnel in the flue-cured tobacco production field.