The vibration of a drill string is the topic under study in drilling and mining engineering. Drill string vibrations cause early failure of bits due to fatigue, drill pipe fracture and bearings damage. A modal and harmonic vibrational analysis of a drill string up to 60-65m long was done in a vertical water well by carrying out parametric studies. This paper investigates vibration of a drill string under longitudinal and mainly lateral which is the most dominant under the action of parameters such as drill pipe lengths and weight on bit. Finite element modelling of a drill string was made in Ansys workbench 2020, mechanical. Modal and harmonic frequencies were determined to obtain optimal drill pipe length and possible weight on bits. The drilling environment was assumed by using different weights on bit.