We present a detailed determination and analysis of 3D stellar mass distribution of the Galactic disk for mono-age populations using a sample of 0.93 million main-sequence turn-off and subgiant stars from the LAMOST Galactic Surveys. Our results show (1) all stellar populations younger than 10,Gyr exhibit strong disk flaring, which is accompanied with a dumpy vertical density profile that is best described by a $sech^n$ function with index depending on both radius and age; (2) Asymmetries and wave-like oscillations are presented in both the radial and vertical direction, with strength varying with stellar populations; (3) As a contribution by the Local spiral arm, the mid-plane stellar mass density at solar radius but 400--800,pc (3--6$^circ$) away from the Sun in the azimuthal direction has a value of $0.0594pm0.0008$,$M_odot$/pc$^3$, which is 0.0164,$M_odot$/pc$^3$ higher than previous estimates at the solar neighborhood. The result causes doubts on the current estimate of local dark matter density; (4) The radial distribution of surface mass density yields a disk scale length evolving from $sim$4,kpc for the young to $sim$2,kpc for the old populations. The overall population exhibits a disk scale length of $2.48pm0.05$,kpc, and a total stellar mass of $3.6(pm0.1)times10^{10}$,$M_odot$ assuming $R_{odot}=8.0$,kpc, and the value becomes $4.1(pm0.1)times10^{10}$,$M_odot$ if $R_{odot}=8.3$,kpc; (5) The disk has a peak star formation rate ({rm SFR}) changing from 6--8,Gyr at the inner to 4--6,Gyr ago at the outer part, indicating an inside-out assemblage history. The 0--1,Gyr population yields a recent disk total {rm SFR} of $1.96pm0.12$,$M_odot$/yr.
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