Electronic Commerce has been a significant commercial phenomenon in recent years, and brings more benefits to people by comparison with the traditional market in aspects of cost, convenience and efficiency. The use of agent technology in e-markets for automatic bargains between buyers and sellers further increases the advantages of the e-market. However, most of existing agent-based bargain strategies assume a fixed number of negotiation participants, which may fail to enlarge agents' profits or to lead a bargain to a success when these strategies are applied in the e-market-based agent negotiations straightway. Problems such as unexpected changes on negotiation participants, possible changes on agents' expected negotiation outcomes, and unexpected switching in-between the buyer's and seller's markets need to be considered in order to guarantee agents' benefits and the success of negotiations. This paper proposes a novel agent negotiation model to help agents to perform a more effective bargain in e-markets by considering the objectiveness of the e-markets and the subjectiveness of the agents. The e-market situation by considering the number of bargain participants is proposed to reflect the objectiveness of the e-markets, and the agents' negotiation attitudes is introduced to indicate agents' responses to possible changes of the e-markets. Both the objectiveness of e-markets and the subjectiveness of agents are taken into account in negotiation procedures such as offer evaluation, negotiation decision making and counter-offer generation. Experimental results on a simulated e-market illustrate the benefits and efficiency of the proposed negotiation model in handling agents bargain problem in complex and dynamic e-market environments.