One-to-many negotiation techniques are unfair because the vulnerable party has a low willingness to participate. Neither the one-to-one nor the one-to-many negotiation scenario considers the mutual influences of negotiation environments or the negotiation participant conditions when both parties change. However, knowledge products are implicit, changeable, and complex. Also the value of knowledge is difficult to assess. Therefore, the levels of understanding vary, and knowledge trading is not always successful. To increase the effectiveness and success of knowledge trading negotiations, this study developed a many-to-many negotiation model for online knowledge trading based on the multiple options available to knowledge suppliers and buyers as well as the repeatable sale of knowledge. This model includes the many-to-many negotiation environment, negotiation specifications, and dynamic negotiation procedures. Therefore, this study designed a multiple-option decision method for making negotiation offer decisions, which is the main activity of the negotiation process. Applying this method can improve the effectiveness of the knowledge negotiation mechanism, thus enhancing the willingness of knowledge suppliers and buyers to conduct online knowledge trading and increase their turnover rates.