Identification of fault in a beam is a challenging hard work for a designer. This paper deals with detection of multi crack in a steel cantilever beam by using theoretical and Experimental results and validate the same with genetic algorithm. Relative mode shape difference and relative natural frequency at different crack location obtain from analytical results and experimental results are used as input data for GA controller. The basic inputs are α1, β1 & α2, β2 with three relative natural frequencies and their relative mode shapes.‘α’represents the relative crack location (L1/L) and β represents the crack depth (b/H). The output of GA controller is αf1, βf1, αf2, βf2. Where αf, βf represents the final relative crack location and final relative crack depth. It has observed that the inverse methodology is a best monitoring tool of detecting crack of a beam.