  In this paper, we consider the exponential Diophantine equation
$a^{x}+b^{y}=c^{z},$ where $a, b, c$ be relatively prime positive integers such
that $a^{2}+b^{2}=c^{r}, r\in Z^{+}, 2\mid r$ with $b$ even. That is $$a=\mid
Re(m+n\sqrt{-1})^{r}\mid, b=\mid Im(m+n\sqrt{-1})^{r}\mid, c=m^{2}+n^{2},$$
where $m, n$ are positive integers with $m>n, m-n\equiv1(mod 2),$ gcd$(m,
n)=1.$ $(x, y, z)= (2, 2, r)$ is called the trivial solution of the equation.
In this paper we prove that the equation has no nontrivial solutions in
positive integers $x, y, z$ when $$r\equiv 2(mod 4), m\equiv 3(mod 4),
m>\max\{n^{10.4\times10^{11}\log(5.2\times10^{11}\log n)}, 3e^{r}, 70.2nr\}.$$
Especially the equation has no nontrivial solutions in positive integers $x, y,
z$ when $$r=2, m\equiv 3(mod 4),
m>n^{10.4\times10^{11}\log(5.2\times10^{11}\log n)}.$$
