Abstract: An online anonymous secret transaction protocol based on anonymous communication is presented to safeguard the privacy of the purchaser in the online transaction. The supplier introduces his commodity information on a bulletin board. The purchaser sends ordering information to the supplier by an anonymous communication mode based on random relay strategy. The purchaser encrypts the ordering information by mixed encryption algorithm. Then he sends it to a transit node which is chosen from the network at random. After receiving it, the transit node sends it to another transit node chosen out at random with a probability P or sends it to the supplier with a probability 1-P. All transit nodes repeat such process of relation until the ordering information arrives at the supplier. Anyone including the supplier, any transit node and any attacker can't get the identity and position of the purchaser. Any transit node or attacker can't get transaction information. The protocol doesn't depend on specified nodes of network. So it can effectively balance network load and improve the stability and reliability. The experiment data show that the protocol can support the safe effective online anonymous secret transaction between purchasers and suppliers. Moreover it owns better robustness.