The hull construction work is composed of many unit processes including template production, marking, flame cutting, fitting, welding and so on. Inaccuracy of the geometry of member is produced during the each unit work ; errors increase at a later stage of the hull construction because of the accumulation of errors. A statistical analysis was made or errors produced during unit processes at various stages of the hull construction. Measurements were made of errors which occurred during the hull construction of an oil tanker and a bulk carrier. It has been proved that the errors follow the Gauss distribution. Values of mean deviation, , and standard deviation, σ, for the each processes were determined. It has been confirmed that the standard deviation of errors observed at a stage of hull costruction can be expressed as the summation of the deviation of errors produced during the preceding stage. Using the result of statistical analysis, the following actions have been made ; 1) The toleran ce of inaccuracy at each of the unit processes has been established. 2) Quality control of each unit process has been established. 3) A standard procedure has been established to minimize the correction which may be required at joints between members to be welded at the erection stage. 4) An attempt has been studied to improve the structual design to minimize joint accuracy at the erection stage.