A precise measurement of the hypertriton lifetime is presented. In this letter, the mesonic decay modes $mathrm{{^3_Lambda}H rightarrow ^3He + pi^-}$ and $mathrm{{^3_Lambda}H rightarrow d + p + pi^-}$ are used to reconstruct the hypertriton from Au+Au collision data collected by the STAR collaboration at RHIC. A minimum $chi^2$ estimation is used to determine the lifetime of $tau = 142^{+24}_{-21},{rm (stat.)} {pm} 31,{rm (syst.)}$ ps. This lifetime is about 50% shorter than the lifetime $tau = 263pm2$ ps of a free $Lambda$, indicating strong hyperon-nucleon interaction in the hypernucleus system. The branching ratios of the mesonic decay channels are also determined to satisfy B.R.$_{(^3{rm He}+pi^-)}/$(B.R.$_{(^3{rm He}+pi^-)}+$B.R.$_{(d+p+pi^-)})$ = $0.32rm{pm}0.05,{rm (stat.)}pm 0.08,{rm (syst.)}$. Our ratio result favors the assignment $J(mathrm{^{3}_{Lambda}H})$ = $frac{1}{2}$ over $J(mathrm{^{3}_{Lambda}H})$ = $frac{3}{2}$. These measurements will help to constrain models of hyperon-baryon interactions.
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