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Radial velocity (RV) is among the most fundamental physical quantitiesobtainable from stellar spectra and is rather important in the analysis oftime-domain phenomena. The LAMOST Medium-Resolution Survey (MRS) DR7 contains 5million single-exposure stellar spectra at spectral resolution $R\sim7\,500$.However, the temporal variation of the RV zero-points (RVZPs) of the MRSsurvey, which makes the RVs from multiple epochs inconsistent, has not beenaddressed. In this paper, we measure the RVs of the 3.8 million single-exposurespectra (for 0.6 million stars) with signal-to-noise ratio (SNR) higher than 5based on cross-correlation function (CCF) method, and propose a robust methodto self-consistently determine the RVZPs exposure-by-exposure for eachspectrograph with the help of \textit{Gaia} DR2 RVs. Such RVZPs are estimatedfor 3.6 million RVs and can reach a mean precision of $\sim0.38\,\mathrm{km\,s}^{-1}$. The result of the temporal variation of RVZPsindicates that our algorithm is efficient and necessary before we use theabsolute RVs to perform time-domain analysis. Validating the results withAPOGEE DR16 shows that our absolute RVs can reach an overall precision of0.84/0.80 $\mathrm{km\,s}^{-1}$ in the blue/red arm at $50<\mathrm{SNR}<100$,while 1.26/1.99 $\mathrm{km\,s}^{-1}$ at $5<\mathrm{SNR}<10$. The cumulativedistribution function (CDF) of the standard deviations of multiple RVs($N_\mathrm{obs}\geq 8$) for 678 standard stars reach 0.45/0.54, 1.07/1.39, and1.45/1.86 $\mathrm{km\,s}^{-1}$ in the blue/red arm at 50\%, 90\%, and 95\%levels, respectively. The catalogs of the RVs, RVZPs, and selected candidate RVstandard stars are available at\url{https://github.com/hypergravity/paperdata}.

Self-consistent Stellar Radial Velocities from LAMOST Medium-Resolution Survey (MRS) DR7