In In this paper, the new type of NAT is firstly discoveredand the associated traversal method is also firstly proposed. This new type is named as "asymmetric cone". The behavior of "asymmetric cone" is different from "full cone", "restricted cone", "port-restricted cone" and "symmetric cone". However, the behavior of the "asymmetric cone" fully follows and matches the NAT standard (RFC-1631, 3022). In the "asymmetric cone", the outbound packet is strictly inspected. Its behavior is like the "symmetric cone". Nevertheless, the inbound packet is loosely inspected. It is like the "full cone", "port restricted cone" or "restricted cone". Thus, the NAT type can be increased to 7 types.Except for the traditional 4 types, those extra 3 types are "asymmetric full cone", "asymmetric restricted cone", and "asymmetric port restricted cone".In the NAT traversal approach, the STUN algorithm was proposed by IETF to traversal the "full cone" and "port restricted cone". However, the STUN algorithm can be worked on the "asymmetric full cone" and "asymmetric port restricted cone". In this paper, a NAT traversal algorithm for the "asymmetric cone" is also firstly proposed in this paper. The theoretic analysis and experimental results confirm the performance of our NAT traversal algorithm in "asymmetric cone".