The effects of soil pH, soil moisture and environmental temperature on the dynamics of benzro[a]pyrene (B[a]P) in long-term contaminated farm land soil were investigated by indoor cultivation. The results showed that B[a]P in soil could be degraded by indigenous microorganisms and the process was influenced greatly by soil pH, soil moisture and environmental temperature. B[a]P in soil was degraded by 43.8%, 37.8% and 14.0% respectively within 7 days' slurry reaction under the conditions of initial pH values of 4.6, 5.9 and 7.3. B[a]P degradation rates were 42.5%, 96.6%, 96.3% and 34.3% within 80 days' incubation under 28℃ with soil moisture of 22%, 43%, 65% and 87% of field water capacity (FWC). The half-time of B[a]P in soil were 33 days and 16 days under the environmental temperature of 25℃ and 40℃, while soil pH was 4.5 and soil moisture was 60% ± 5% of FWC. Therefore, environmental conditions such as soil pH, soil moisture and environmental temperature affected the biodegradation of B[a]P in soil greatly and the degradation of B[a]P could be enhanced by environmental regulation.