Abstract: In order to have the time to reach the optimum outburst elimination effect after the hydraulic loosening measures made, the time effect of the measures t 0 the outburst elimination effect was investigated.The paper first provided the conception of the time effect. The paper analyzed the existed cause and the investigation necessity.With the site investigation on the outburst predicted index and the related parameters at different time after the water injection completed, the outburst predict ed indexes and the gas emission quantity variation law were obtained and the outburst eliminated mechanism and the outburst eliminated time effect features after the hydraulic loosening measures conducted were analyzed. The results showed that after the hydraulic loosening measures conducted, the outburst predicted index and th e actual measured value of the gas emission quantity would ne obviously reduced with the time passed and there would be a certain time effect.At three hours before th e hydraulic loosening measures conducted, the outburst predicted index and the gas emission quantity would be reduced obviously.After 34 hours of the measures cond ucted, the outburst predicted index and the gas emission quantity would be basically not changed.The paper held that the shortest time to reach the optimum outburst e limination effect after the hydraulic loosening measures made in Chengzhuang Mine would be 34 hours.