In this study, an electro-optical simulation method is developed to predict the light intensity distribution and luminous flux of an in-house fabricated GaN based blue LED chip. The entire modeling process links an electrical simulation with ANSYS and optical simulation with LightTools, by assuming a proportional relation between the distributed current density and light emission energy on the multiple quantum well (MQW) layer. Experimental results show that the proposed simulation method can give a good prediction on the light intensity distribution for a semi-packaged GaN based blue LED chip. Further analysis on the simulation results reveals that an increase of at most 8% of the luminous flux can be achieved when the current density is controlled to evenly distribute on the MQW layer whereas the chip structure and electro pattern remains the same.