According to feature of hydrology in northwest region of China,three paramers α,β and γ can be used to study river runoff distribution,α= W_4-8/W_7-9 here W_4-8—total runoff volume from April to June,W_7-9—total runoff volume from July to Sept..α can be explained as a ratio of volume of season snow melt to glacial melt at high mountains and rain volume in total annual runoff.
β=W_4-8/W_10-3
here W_4-9—total runoff volume from April to Sept.,W_10-3—total run off volume from Oct.to next March..β can be explained as a ratio of flood runoff volume to non flood runoff volume,also a ratio of supply of ground water tototal annual runoff volume. The parameter γ,can be estimated by
γ=(α-α)/σ_α
here α—long term average annual α,σ_α—mean square error of α. The paper used the three parameters to make preliminary an approach to the classification of rivers in northwest region of China.