[Objective]The paper was to study effect of Lupo compound microemulsion( LCW) on Alternaria alternata. [Method]The activity of spore germination and mycelial growth was investigated by filter paper method and mycelial growth rate method,and field test was also conducted to determine the effect of LCW on tobacco plants. [Result]LCW could inhibit spore germination and mycelial growth of A. alternate. The higher concentration led to more severe reduction of sporulation and heavier inhibition against mycelial growth. When LCW was diluted into 200 times,inhibition rate of sporulation reached 91. 23%,and the inhibition rate of mycelial growth reached 93. 50%. Field test also proved that LCW had significant inhibitory effect on tobacco brown spot disease. [Conclusion]The study provided the reference for using botanical pesticide to control A. alternate in fields. [Objective] The paper was to study effect of Lupo compound microemulsion (LCW) on Alternaria alternata. [Method] The activity of spore germination and mycelial growth was investigated by filter paper method and mycelial growth rate method, and field test was also conducted to determine the effect of LCW on tobacco plants. [Result] LCW could inhibit spore germination and mycelial growth of A. alternate. The higher concentration led to more severe reduction of sporulation and heavier inhibition against mycelial growth. When LCW was diluted into 200 times, inhibition rate of sporulation reached 91. 23%, and the inhibition rate of mycelial growth reached 93. 50%. Field test also verifies LCW had significant inhibitory effect on tobacco brown spot disease. [Conclusion] The study provided the reference for using botanical pesticide to control A. alternate in fields.