  We analyzed 186 binary pulsars (BPSRs) in the magnetic field versus spin
period (B-P) diagram, where their relations to the millisecond pulsars (MSPs)
can be clearly shown. Generally, both BPSRs and MSPs are believed to be
recycled and spun-up in binary accreting phases, and evolved below the spin-up
line setting by the Eddington accretion rate ($\dot{M}{\bf \simeq}10^{18}
g/s$). It is noticed that most BPSRs are distributed around the spin-up line
with mass accretion rate $\dot{M}=10^{16} g/s$ and almost all MSP samples lie
above the spin-up line with $\dot{M}\sim10^{15} g/s$. Thus, we calculate that a
minimum accretion rate ($\dot{M}\sim 10^{15} g/s$) is required for the MSP
formation, and physical reasons for this are proposed. In the B-P diagram, the
positions of BPSRs and their relations to the binary parameters, such as the
companion mass, orbital period and eccentricity, are illustrated and discussed.
In addition, for the seven BPSRs located above the limit spin-up line, possible
causes are suggested.
