The objective of this paper is to reconstruct the construction process found in the nave of the Cistercian church of Sénanque in the medieval time. After our precedent papers which treat the chapter house, and also the choir and transept, the present paper also tends to analyze the irregularities and measures found in the nave of this church in order to restitute what happened in the real construction site. The nave of the Sénanque church contains the several well known irregularities such as the positional discrepancy of the pilaster and the transvers arches in the aisles.<br> The authors once approved the fact that previous literatures insist that the nave is constructed in the second phase between ca. 1185 and 1200. This argument which could be admitted as a general vision is re-examined in this paper through the minute and detailed observation and analysis on the optical irregularities and on the measures based on the authors' own measuring the church.<br> The shape of windows, the joints of stones, the profiles of the cornice and also the masonry of the walls and vaults are the repertories which we examined first to deduce the irregularities as the elements possible to explain the construction process. After that we proposed the metrological analysis to give a logical explanation of these irregularities, especially the positional discrepancy between the pilasters and transvers arches in the aisles, using the idea of the secondary unite of measure derived from the principal foot, called “pes manualis” attested in the medieval various documents. We attested three principal foots and the six “pes manualis” derived from these three feet.<br> As conclusion, as to the discrepancy between the pilasters and transvers arches in the aisles could be explained by the different two “pes manualis” used respectively for the width of the pilasters and that of transvers arches. And finally we succeeded to attest that, concerning the construction of the vault in the nave, three different phases. The construction period of the central vessel corresponds to that of the squinch dome on the crossing. Concerning the construction phase of the pillar, we also attested the more detailed process which is divided into two different phases. We also might point out that the big change of the initial project of vault of the central vessel caused the many modification of architectural aspect in the whole church, i.e. the heightened vault of the aisles, re-vaulting of apse and transepts, and reconstruction of the dome on the squinchs, and the employment of pointed arch.<br> In the end, as to one of major contributions of this paper to the study on the medieval construction concerning the Cistercian abbey church of Sénanque, we insist the archeological importance of the reading of the irregularities, and of the metrological analysis.