Abstract: Metalaxyl is a fungicide which can translocate basipetally in phloem after absorbed by leaves. In this study, the phloem mobility of metalaxyl was investigated. The Ricinus communis seedling was used as the model plant. The contents of metalaxyl in the phloem sap under different culture conditions were detected by gas chromatography and mass spectrometry (GC-MS). Cultural factors such as the concentration of metalaxyl, pH value of buffered solution, incubation temperature, incubation time and light condition were studied. The results indicated that the light has no significant influence on the mobility of metalaxyl in phloem sap of R.communis. And under the experimental conditions, the highest contents of metalaxyl in phloem of R. communis was observed when the concentration of metalaxyl in the incubation solution was 400 mg/L. The highest contents of metalaxyl in phloem of R. communis was observed when the pH value of incubation solution was 5.5. And the optimal incubated temperature was 28 ℃, too high or low temperature will reduce the contents of metalaxyl in the phloem of R. communis. The contents of metalaxyl in phloem sap increased significantly within the first 3 hours, which was significantly higher than that within the first 2 hours. Suitable conditions for the maximum absorption of R. communis was optimized in this study, and provide a reference for other unknown compounds to detect their phloem mobility in R. communis.