We present estimates of stellar age and mass for 0.93 million Galactic disk main sequence turn-off and sub-giant stars from the LAMOST Galactic Spectroscopic Surveys. The ages and masses are determined by matching with stellar isochrones using Bayesian algorithm, utilizing effective temperature $T_{rm eff}$, absolute magnitude ${rm M}_V$, metallicity [Fe/H] and $alpha$-element to iron abundance ratio [$alpha$/Fe] deduced from the LAMOST spectra. Extensive examinations suggest the age and mass estimates are robust. The overall sample stars have a median error of 34 per cent for the age estimates, and half of the stars older than 2,Gyr have age uncertainties of only 20--30 per cent. Median error for the mass estimates of the whole sample stars is $sim8$ per cent. The huge dataset demonstrates good correlations among stellar age, [Fe/H] ([$alpha$/H]) and [$alpha$/Fe]. Particularly, double sequence features are revealed in the both the age--[$alpha$/Fe] and age--[Fe/H]([$alpha$/H]) spaces. In the [Fe/H]--[$alpha$/Fe] space, stars of 8--10,Gyr exhibit both the thin and thick disk sequences, while younger (older) stars show only the thin (thick) disk sequence, indicating that the thin disk became prominent 8--10,Gyr ago, while the thick disk formed earlier and almost quenched 8,Gyr ago. Stellar ages exhibit positive vertical and negative radial gradients across the disk, and the outer disk of $Rgtrsim$,9,kpc exhibits a strong flare in stellar age distribution.
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