Abstract: A new transformation of modified Bessel function is built in this paper By applying the result of the theorem on the differential and integral calculus to any two equation of the type of this transformation smartly, a general integral formula involving the product of two modified Bessel functions is obtained.Furthermore, by recurrence relations of modified Bessel function, we get the analytical expressions of two kinds of integrals are gotten respectively, which can be widely used in the evaluation of the power in the electromagnetic fields.