The conventional study of soil physicochemical properties often relies on the ex-situ sampling and determination, failing to reflect the soil environment's heterogeneity because of the destructive sampling processes. The process disturbs the original structure and ignores the heterogeneity of soil microsites. In recent years, planar optode with high spatiotemporal resolution has gained more attention in investigating soil biogeochemical processes. Based on the luminescence principle, the specific luminescent indicator that is sensitive to different solutes is embedded into the matrix to make a sensing membrane, then records its two-dimensional emission signals using digital imaging technology. Therefore, high resolution and sensitive dynamic characteristics of solutes can be continuously obtained by changing the indicator luminescence signal with relatively simple experimental configurations. So far, planar optode has been successfully deployed to monitor the dynamics of O₂, pH, CO₂, NH₄⁺ and other important physicochemical parameters in soil. This paper introduced the main compositions of planar optode system, listed the methods of quantitative analysis, reviewed the main capabilities and limitations and summarized the main applications of planar optode in the study of soil microscale heterogeneity. Further, opportunities of planar optode were discussed for future development and applications in soil science and agricultural environment.