The remote pumped amplifier is the key component of ultra-long span unrepeated all-optical communication system. The basic principle of the remote pumped amplifier (ROPA) is introduced. A practical remote pumped Erbium doped fiber amplifier design scheme suitable to the ultra-long span unrepeated all-optical communication system is proposed. And with practical test conclusion and software simulation result, the problems influencing remote pumped amplifier gain are analyzed and discussed. The conclusion can be used as an important reference for the ultra-long span remote pumped amplified system design.