Abstract: A low-silicon defoaming agent for delayed coking was developed, which is a complex additive package containing polyether modified polysiloxane mainly. The polyether modified polysiloxane was prepared from hydrogenous silicone oil and polyether, with FA-2 as catalyst. The influences of reaction conditions, such as reaction time, reaction temperature, the ratio of reagents and catalyst dosage were studied, and the optimum conditions were obtained as follows: the mole ratio of Si-H in hydrogenous silicone oil and –OH in polyether was in the range of (1:1.4)—(1:1.6), the mass fraction of catalyst was 0.4 %, reaction was proceeded at 110 ℃ for 8 h. Performance evaluation results showed that the prepared polyether modified polysiloxane and its complex exhibited good antifoaming and suppressing foam performance.