The integrated polymer optical readout has been recognized as a promising route to obtain miniaturized cantilever-based sensor works on static mode for various liquid-state chemical and biological measurements in portable lab-on-chip systems. For conventional optical readouts based on end-fire coupling mechanisms, the most sensitive region was limited to a cantilever deflection of several micrometers due to the Gaussian profile of the mode in polymer waveguides. We proposed an integrated optical readout based on a hybrid plasmon directional coupler aiming at improving the sensitivity at the sub-micrometer deflection region (<1 μm). The coupler consists of a short-range surface plasmon waveguide and a polymer waveguide. We show that the coupling length and the propagation loss of the coupler are ultra-sensitive to the deflection, which leads to improved sensitivity of the readout. In addition, the dynamic range can be extended by integrating an array of hybrid plasmon directional couplers onto a single microcantilever. The proposed optical readout is beneficial to high sensitivity cantilever-based sensors for lab-on-chip applications and enables the design of more compact optical waveguide-based sensors in water.