This study provides a detailed investigation of the deformation behavior and microstructural evolution of a high yield ratio of 0.88 in complex phase (CP) steel produced by the compact strip production (CSP) process which is aimed for application in automotive industry. A similar alloy composition of CP steel with a lower yield ratio of 0.82 was produced by conventional continuous rolling (CCR) process as a reference. Both steels consist of ferrite, bainite, and martensite–austenite (MA) constituents, while the volume fraction of MA constituents is around 17% and 5% in CCR steel and CSP steel, respectively. Interrupted tensile experiments showed that at the early stage of deformation (< 2% true strain), dislocation proliferation is more significant in CCR steels than CSP steels, mainly due to the accumulation of geometrically necessary dislocations (GNDs). Cyclic load–unload–reload tensile tests show that heterogeneous hardening is the main strengthening mechanism of CSP steels during the homogeneous plastic deformation stage at > 2% true strain although the value of hardening is not significant. The mediocre effect of heterogeneous strengthening is attributed to the low volume fraction of MA constituents which introduces fewer heterogeneous interfaces in CSP steels and reduces the pile up of GNDs at the interfaces during the uniform plastic deformation process. The heterogeneous hardening mediocrely and its domination in hardening contribute to a high yield ratio in CSP steel. The obtained understanding demonstrates the feasibility of obtaining a high yield ratio by improving the homogeneity of multiphase materials which booming the applications of heterogeneous materials.