To reduce the great losses caused by gas explosions in the gas transportation process and to improve the explosion venting efficiency in pipelines, a small pipeline with both a side vent and an end vent was developed, and premixed methane/air explosion characteristics were studied in the pipeline with different side venting areas. The experimental results show that in the same side venting position, with an increasing venting area, the propagation time for flames through the pipeline increases on a large scale, the peak overpressure of the methane explosion drops significantly, and the venting effect is greatly enhanced. Meanwhile, when the flame propagates upstream a side vent, the propagation can be slightly promoted by a side vent with a small area in the corresponding period of time, whereas a side vent with a large area can hinder the flame propagation all the time. After the flame passes the side vent, side venting plays a strong role in flame propagation, and the flame propagation velocity drops rapidly under a large side venting area. It is also found that overpressure in the vicinity of a side vent is less affected by the side venting area, while the effect of the venting area on overpressure is relatively large at a far distance from the side vent position.