It is summarized that the electron spectrum in superlattices being studied for many years and the results researched. To study the electron spectrum in superlattices
the coefficients of transmission and reflection are introduced for aperiodic and periodic superlattices. The electron spectrum in superlattices under external electric field is shown. The external condition could induce the change of piezoelectric field in superlattices and further induce the change of tunneling current.