Abstract: Farmers' income growth is an important foundation to achieve a comprehensive well-off society and it is also critical for increasing domestic demand and promoting sustainable economic growth. Based on Cobb-Douglas distribution function, using panel data Granger causality test and spectral analysis, this paper analyzed GDP and industries’ contributions to farmers’ income growth. Empirical analysis results show that 1) in the static panel data model, GDP, primary industry, and secondary industry significantly contributed to farmers' income growth, but the contribution of the tertiary industry growth is not significant; 2) in the dynamic panel data model, GDP and all the industries’ growth are the Granger causes of the farmers’ income growth; 3) farmers' income growth is affected by the fluctuations of agricultural and non-agricultural industries; 4) the main fluctuation cycle for GDP, secondary and tertiary industries is 7-12 years, but the fluctuation cycle of the first industry is only 2.8 years; and 5) the frequent fluctuations in agricultural industry increase the volatility of farmers’ income. To maintain the stable growth of farmers’ income, it is suggested that in-depth economic reform, opening up, steady economic growth, stable agricultural production, strengthening agricultural risk control, and promoting urbanization process are necessary.