An efficient hull form design needs to incorporate some prediction methods which will be able to predict the influence of hull form modification on the ship performance. This paper presents a new and simple prediction method for the form factor which relates directly to the hull form. Six flow-field parameters which have influences on the form factor are proposed on the basis of the result of double-model flow calculation and 3-dimensional boundary layer calculation around the hull form. A regression equation to predict the form factor is made by using 7 parameters (6 flow-field parameters and displacement-length ratio) and model test results in a towing tank. In order to adopt the minimum Akaike Information Criterion (AIC) estimate method in a regression analysis, 7 parameters are selected among many variations. Predicted results for the form factor of full form ship at full load condition by the present regression equation show good agreement within 2% with tank test results. At ballast condition, predicted results show good agreement within 3%. Since flow-field parameters in the present regression equation act as intermediary between actual hull form and ship performance, a designer can easily obtain an information of how to modify the hull form according to the flow-field parameter in order to improve ship performance.