Optical gain characteristics of Erbium doped Silicon Rich Silicon Oxide(SRSO) optical waveguide amplifier was investigated. Er doped SRSO thin films, which consist of Si nanoclusters embedded inside a $SiO_2$ matrix, were prepared by electron cyclotron resonance plasma enhanced chemical vapor deposition with co-sputtering of erbium target. We found that thermal annealing of SRSO film at ~ 950℃ for 5minutes result in long lifetime and strong luminescence film suitable for making waveguide amplifier by forming high quality nanocrystals and removing defect states inside silica. It is estimated that optimum composition for waveguide amplifier is 1 at.% excess Si and ~ 0.03 at.% Er. Photoluminescence excitation spectrum showed that Er in SRSO can be very efficiently excited by earning the energy from silicon nanocrystal absorbing pumping signal, through which mechanism Er in SRSO can emit 1540nm light much more efficiently than that in silica. Ridge type-single mode waveguide was made out of Er doped SRSO thin film with above condition by chemical etching using BOE and mechanically polished to couple light signal efficiently. Signal enhancement was measured by pumping the ridge waveguide on the top with 477nm Ar ion laser line, not Er optical absorption band. Huge enhancement which cannot be explained by Er in glass confirms that gain in Er doped SRSO waveguide amplifier is attributed to Er interacted with nanocluster. From simulation using absorption spectrum, signal enhancement curve and rate equation it was concluded that Er emission crosssection at 1535nm is $1.7× 10^{-19}㎠$, larger than that of silica by an order of magnitude. From gain curve analysis for pumping flux, effective absorption crosssection of Er in SRSO at 477nm was $\simeq$ $10^{-17}㎠$. It is also four orders of magnitude larger than that of Er direct absorption excitation. It is confirmed that free carrier loss due to the free carrier from silicon nanocrystal was suppressed by showing there are n...