An evaporation disk model is proposed_to figure out shapes of molecular disks with density distributions of ρ_d∝r^(-n)(n$gt;1.8) using the energy and pressure equilibrium conditions as well as to explain the collimation mechanism of optical and radio jets with an openning angle of about 10 inside bipolar molecular outflows. Numerical hydrodynamic calculation of the jet inside shows that the jet velocity increases with a dependence on z^(1-5) and the Mach number of the jet converges to √3 . Mechanical energy of the jet heats the jet material, increasing the jet temperature with a distance. Calculated Ha flux in shock condition and radio continuum intensity at 5GHz are surely comparable to the observed ones. These results strongly support the evaporation disk model in collimating jet.