Abstract: Reservoir size sequential analysis is based on Pareto principle. The key and the difficulty is acquiring the value of coefficient as ‘k’ which describes the gradient in variation of resource scale, which restricts the effectiveness of corresponding method. Through calculating ratio of the scales of the discovered resources and applying the possible sequential number, a specific optimized methodology is proposed. It mainly includes establishing the cross plot with the axes of sequential number and k according to the calculated ratio, searching and locating the combination of data points from different ratio which can form an approximately straight and vertical line against the k axis, and acquiring the value in the k axis for the intersection as a solution of k. The principles in optimizing and determining the result after acquiring the solution set to satisfy the need in resource assessment are furtherly suggested. From the re-analysis about the classic data set from open published academic literature, it presents that applying related method can effectively acquire the value of such coefficient (k). An actual application about tight gas contained in reservoir as 6th group of Jurrasic Shaximiao formation in Yanting block of Jinqiu gas-producing area located in the center part of Sichuan Basin is also provided as further support. The linear relevant fitting result is favorable between forecast outcome and actual data. The calculated result of resource scale of this case is consistent with current recognition from tight gas exploration in Sichuan Basin. This methodology is with serval advancements, which includes low dependency on geological experience, no demand in setting analytic step size or complicated determinant and matrix manipulation. The subjectivity and calculative complexity in deciding the key parameters are effectively reduced. Corresponding algorithm is achieved to be coded as computer program. The efficiency is accordingly promoted. It can be helpful in further application of reservoir size sequential method.