The relationship between moment, probability-weighted moment (PWM) and linear-moment (L-moment) is deseribed and is il-lustrated with gamma distribution in this paper. The L-moment is the linear combination of the PWM and the computed results from both methods are exactly same. The PWM and L-moment are all related to specific distribution types and probabilities as weights, and their re-sults have lower sensitivity. The approximated formula of the computed parameters and their accuracy are analyzed in detail. In hydrologie application, the computed results may only be used as initial values for estimation and should be used after the reasonable analysis.