  High-mass gamma-ray binaries consist of a presumptive pulsar in orbit with a
massive star. The intense outflows from the star can absorb radio emission from
the pulsar, making the detection of pulsation difficult. In this work, we
present the basic geometry and formulae that describe the absorption process of
a pulsar in binary with an O/B star and apply our model to two typical and
well-studied binaries: PSR~B1259-63/LS~2883 and LS 5039. We investigate the
influences of the equatorial disc of LS 2883 with different orientations on the
dispersion measure and free-free absorption of the radio pulsation from PSR
B1259-63. The observed data are consistent with the disc inserted on the
orbital plane with a relatively large inclination angle. For LS 5039, due to
its tight orbit, it was believed that the strong wind absorption makes
detecting radio emissions from the putative pulsar unlikely. However,
considering the wind interaction and orbital motion, a bow shock cavity and a
Coriolis shock would be formed, thereby allowing the pulsations to partially
avoid stellar outflow absorption. We investigate the dependence of the radio
optical depth on the observing frequencies, the orbital inclination angle, and
the wind parameters. We suppose that the presumptive pulsar in LS 5039 is
similar to PSR B1259-63 with pulsed emission extending to several tens of
gigahertz. In that case, there could be a transparent window for radio
pulsations when the pulsar is moving around the inferior conjunction. The
following deep monitoring of LS 5039 and other systems by radio telescopes at
high radio frequencies might reveal the nature of compact objects in the
future. Alternatively, even a null detection could still provide further
constraints on the properties of the putative pulsar and stellar outflows.
