Double NAT

What do two-way NAT do on Huawei and what do they do on Huawei's two USG6600? The first firewall is the conversion of the internal network into the internal network address, and the second firewall is the conversion of the internal network into the external network address, and then out of the public network, so that all the intranet devices in the first firewall can go out to the public network and access the public network, but now I have done an experiment. The packet has gone straight to, and the second firewall will not go down, so I would like to ask what is the situation. Please help me solve it. Thank you!

I have made two-way routing assignments on the router, have done static, but always can not access R4, do not know the reason, please help to see.

Attachment: http://down.51cto.com/data/2368020