The distribution of initial fragment velocity in the aim direction is one of the important factors for evaluating the power of the directional warhead. Therefore， the calculation method of the initial fragment velocity in the whole domain on the directional side of the warhead under the eccentric double-line initiation and the kinetic energy gain compared with the central initiation are studied. Based on the infinitesimal theory， the calculation method of the initial fragment velocity in different circumferential position on the directional side was derived， and the static explosive experiment of the warhead was carried out to compare with the theoretical result. Combined with the numerical result of the warhead， the axial velocity correction function was fitted， and the universality of the algorithm was verified according to the existing research. It is shown that the proposed formula is suitable for the warhead with eccentric double-line initiation， and the error between theoretical calculation and test results is within 4.80%， calculation result is consistent with actual situation. The fitting correction function can predict the initial velocity of the fragments in different axial direction. The algorithm still has good universality when the warhead parameters change and the calculation error is less than 7.11%. Compared with central initiation， the eccentric double-line initiation mode with an angle of 60° can increase the total kinetic energy of the fragments in the range of -30°-30° from the center of the directional side by 34.9%.