PurposeOn the basis of principal-agent and financing constraints theories, the purpose of this paper is to construct a unified research framework via mathematical models and to provide a logical and consistent explanation of the contradictory discovery of the relationship between dividend payment and I-CFO in the previous literature.Design/methodology/approachEstablishing the economic mathematical models, this paper uses the comparative static analysis to figure out the equilibrium results, to further testify the conclusions, the authors initiate the empirical tests to make the discussion more realistic.FindingsThe authors observe that overinvestment caused by agency problems is the primary reason for I-C sensitivity when the investment expenditure is less than the internal capital; dividend payout suppresses the overinvestment caused by the agency problem, thus alleviating the investment’s dependence on the internal capital. However, underinvestment caused by the financing constraints is the primary cause of I-C sensitivity when the investment expenditure is greater than the internal capital. The payment of cash dividends increases the investment shortage caused by the financing constraints, thus increasing the sensitivity. Further, the authors explore the impact of dividend payments on I-CFO sensitivity. They argue that dividend payment is not an appropriate measure of financing constraints. Both I-CFO sensitivity and I-C sensitivity are functions of agency cost and information cost.Research limitations/implicationsThis study provides a logical and consistent explanation of the contradictory discovery of the relationship between dividend payment and I-CFO in the previous literature and provides a clear framework and reference for future studies on the impact of financial constraints, agency cost on the investment’s dependence on the internal capital.Practical implicationsThe theoretical model of this paper supports this differentiated mandatory dividend policy and provides reference and evidence for China's financing policies and dividend distribution policies.Originality/valueThis study theoretically and empirically analyzes and verifies the roles of agency cost and financial constraints on the determinants of I-C sensitivity for the first time. First, different from earlier literature, this paper puts forward I-C sensitivity as a new measure of investment’s dependence on internal capital, making the measurement more accurate. In the case of a firm with positive liquidity reserves, using the I-CFO sensitivity as a measure of external financing constraints could overestimate the firm’s financial constraints. Second, by constructing an economic static analysis framework, this study analyzes how I-C and I-CFO sensitivities change with the agency cost, the financing constraints and the dividend payment ratio. The research provides a basic framework and explanation on the contradictions of the earlier literature. The results are supposed to serve as a foundation for estimations of investment’s dependence on internal capital and should be embedded in general empirical tests in future research.