Ageratum conyzoides is a detrimental weed in the low-altitude farmland and orchards of south China. To elucidate the adaptive ability of A. conyzoides in the environment and its perniciousness, studies were conducted to evaluate the influence of different environmental factors, including light, temperature, pH, humidity, and osmotic potential, on seed germination and seeding emergence of Ageratum conyzoides. The results showed that: (1) seeds could germinate from 10 ℃ to 30 ℃ with the optimum temperature being 20 ℃. Additionally, alternating temperature could increase the rate of seed germination. (2) Seeds of A. conyzoides were sensitive to light, and it was difficult for seeds to germinate without light. (3) The rate of seed germination was higher than 55% when the soil relative humidity was in the range of 50%-100%, with the optimum relative humidity being 70%. (4) Seeds could germinate at the soil surface, and emergence was inhibited if seeding depth reached 1 cm. (5) The seed germination rate reached 85% when pH was in the range of 5-10, with the optimum pH being 7. (5) When the concentration of NaCl was at 0-80 mmol/L, seed germination rate was above 88%, while germination was 30% at salinity level of 160 mmol/L. (6) When osmotic potential was -0.40-0 MPa, the germination rate reached 70%, but no germination occurred at osmotic potentials of -0.6 Mpa. Therefore, it could be inferred that A. conyzoides showed strong adaptiveness to the different environments. As such, it could cause early damage to crops.