To solve the problem of uncertain investigation depth of the original logging curves electromagnetic LWD Resistivity

instrument，this paper studied on synthesizing the original logs into curves with fixed depth of investigation. We firstly

used a simple and fast iterative inversion algorithm for shoulder-bed correction，followed by Gauss Newton-gradient descent

algorithms to inverse invaded formation resistivity，true formation resistivity and invasion radius for each layer. Then according

to the concept of the pseudo spacing，we drew the chart of investigation depth and source spacing，source spacing and apparent

resistivity by using the three parameters obtained before. Finally we obtained curves with fixed depth of investigation by

interpolation. Through a series of numerical simulation，we found that the different curves which were synthesized showed the

separation phenomenon with regularity in the invaded formation，which coincided with the geological characteristics well，and

can reflect invasion characteristics more directly compared to the original curves. So this method could improve the application

effect of this kind of instrument，and can be compared with the array induction curves，which makes geological interpretation

on formation evaluation more accurately.