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We present a detailed determination and analysis of 3D stellar massdistribution of the Galactic disk for mono-age populations using a sample of0.93 million main-sequence turn-off and subgiant stars from the LAMOST GalacticSurveys. Our results show (1) all stellar populations younger than 10\,Gyrexhibit strong disk flaring, which is accompanied with a dumpy vertical densityprofile that is best described by a $sech^n$ function with index depending onboth radius and age; (2) Asymmetries and wave-like oscillations are presentedin both the radial and vertical direction, with strength varying with stellarpopulations; (3) As a contribution by the Local spiral arm, the mid-planestellar mass density at solar radius but 400--800\,pc (3--6$^\circ$) away fromthe Sun in the azimuthal direction has a value of$0.0594\pm0.0008$\,$M_\odot$/pc$^3$, which is 0.0164\,$M_\odot$/pc$^3$ higherthan previous estimates at the solar neighborhood. The result causes doubts onthe current estimate of local dark matter density; (4) The radial distributionof surface mass density yields a disk scale length evolving from $\sim$4\,kpcfor the young to $\sim$2\,kpc for the old populations. The overall populationexhibits a disk scale length of $2.48\pm0.05$\,kpc, and a total stellar mass of$3.6(\pm0.1)\times10^{10}$\,$M_\odot$ assuming $R_{\odot}=8.0$\,kpc, and thevalue 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\,Gyrat the inner to 4--6\,Gyr ago at the outer part, indicating an inside-outassemblage history. The 0--1\,Gyr population yields a recent disk total {\rmSFR} of $1.96\pm0.12$\,$M_\odot$/yr.

Stellar mass distribution and star formation history of the Galactic disk revealed by mono-age stellar populations from LAMOST