Enriched gas miscible displacement is one of the main methods for further improving waterflooding recovery. Because of LPG consisted of enriched gas is expensive, if non-miscible displacement is not used or gas breakthrough are occurred during displacing, injected mixed gas will be produced without miscible effect on remaining oil and cause huge economic waste. Therefore, real-time monitoring displacement dynamic, initiative adjusting and guaranteeing the reservoir to always be a miscible displacement are particularly important. In this paper, taking the enriched gas miscible displacement in one oilfield of North Africa as an example, the practical methods of judging miscible displacement, including pseudo-ternary phase diagrams, injection composition, reservoir condition, produced GOR and produced gas component, are studied. The results show that pseudo-ternary phase diagrams drew based on phase equilibrium calculation can not only clearly show MCM process, but also can determine the MMC and MMP. In order to achieve enriched gas miscible displacement, we have to make sure that the injection pressure, temperature and enriched gas component can meet the miscible requirements or not, while monitoring produced GOR and C3，C4 intermediate component changing in produced gas, and taking this as the main basis for judgment. Produced GOR is strongly affected by reservoir physical property, therefore, it can be taken as a secondary basis for judgment. At last, the parameters at the injection end can be adjusted based on the judgment results.
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