  In this paper we calculate the spectrum of Neumann matrix with zero modes in
the presence of the constant B field in Witten's cubic string field theory. We
find both the continuous spectrum inside $[{-1\over3}, 0)$ and the constraint
on the existence of the discrete spectrum. For generic $\theta$, -1/3 is not in
the discrete spectrum but in the continuous spectrum. For each eigenvalue in
the continuous spectrum there are four twist-definite degenerate eigenvector
except for -1/3 at which the degeneracy is two. However, for each
twist-definite eigenvector the twist parity is opposite among the two spacetime
components. Based upon the result at -1/3 we prove that the ratio of brane
tension to be one as expected. Furthermore, we discuss the factorization of
star algebra in the presence of B field under zero-slope limit and comment on
the implications of our results to the recent proposed map of Witten's star to
Moyal's star.
