Abstract:The ultimate goal of geological modeling is to set up a reasonable geological model and characterize the uncertainty of reservoir and reserves. The South China Sea P gas field is at the stage of early study and its well data is lack, the lateral and vertical variety of reservoir is very quick, so the uncertainty of the reserve is very strong. This paper discussed the method for the uncertainty of reserve based on geology model, then the general method about the uncertainty of similar gas field has been summarized. Through analysis on the sensitivity about the variable, the main variable has been determined. Based on this study, reserve evaluation and optimization of geological model have been done by Latin Hypercube Sampling. At last the change of structure and OWC is defined as the main factor affected the reserve of the gas field, and P50 is the producing reserve. The method provide a new thought for reserve utilization at the stage of early study.