  In supersymmetric models a gluino can decay into tb\tilde{\chi}^{\pm}_1
through a stop or a sbottom. The decay chain produces an edge structure in the
m_{tb} distribution. Monte Carlo simulation studies show that the end point and
the edge height would be measured at the CERN LHC by using a sideband
subtraction technique. The stop and sbottom masses as well as their decay
branching ratios are constrained by the measurement. We study interpretations
of the measurement in the minimal supergravity model. We also study the gluino
decay into tb and \tilde{\chi}^{\pm}_2 as well as the influence of the stop
left-right mixing on the m_{bb} distribution of the tagged $tb$ events.
