Starting with a given function $k$, as the kernel of a convolution operator, the auxiliary function $ H $ is constructed, which is the kernel of a normal operator. Establishing the connection between this operator and the previous one, the exact asymptotic of singular values is obtained. The method is used to find the exact asymptotic of the singular values of integral operators with the kernel of the form $T(x,y)k(x=y)$, where $k$ is not necessary a homogeneous function.