Precise determination of flow vector (flow rate and direction) is essential for advancing millimeter-scale in situ fluid monitoring. However, existing monitoring methods are fundamentally constrained by measurement principles and structural design, limiting their miniaturization, integration, and in situ monitoring. Although triboelectric nanogenerators provide unique advantages for miniaturized in situ monitoring, they fail to deliver effective signal outputs under continuous fluid conditions. Here, we propose an in situ and real-time strategy for quantitative flow vector measurement of continuous fluid, based on liquid-semiconductor interfacial electrification. By exploiting competitive electric fields at the liquid-semiconductor interface generates a direct-current signal that simultaneously encodes flow, both the magnitude and direction, establishing a robust foundation for continuous monitoring. Guided by this mechanism, a continuous-fluid tribovoltaic nanogenerator (CF-TVNG) that integrates a free-standing mode structure with piping systems is designed, achieving coefficients of determination (R2) exceeding 0.99 for both forward and reverse flows. Furthermore, an automated in situ monitoring system is implemented using a Python program, enabling real-time flow vector analysis and abnormal condition alerts. This work presents a compact and scalable approach to self-powered continuous-flow monitoring, offering broad potential for applications in biomedical diagnostics and pipeline monitoring.