  In this paper, we firstly give the definition of dipersionless bigraded Toda
hierarchy (dBTH) and introduce some Sato theory on dBTH. Then we define
Orlov-Schulman's $\M_L$, $\M_R$ operator and give the additional Block symmetry
of dBTH. Meanwhile we give tau function of dBTH and some some related
dipersionless bilinear equations.
