We present results of a combined analysis in neutrino oscillations without unitarity assumption in the $3 u$ mixing picture. Constraints on neutrino mixing matrix elements are based on recent data from the reactor, solar and long-baseline accelerator neutrino oscillation experiments. The current data are consistent with the standard $3 u$ scheme. The precision on different matrix elements can be as good as a few percent at $3sigma$ CL, and is mainly limited by the experimental statistical uncertainty. The $ u_e$ related elements are the most precisely measured among all sectors with the uncertainties $<20%$. The measured leptonic CP violation is very close to the one assuming the standard $3 u$ mixing. The deviations on normalization and the unitarity triangle closure are confined within $mathcal{O}(10^{-3})$, $mathcal{O}(10^{-2})$ and $mathcal{O}(10^{-1})$, for $ u_e$, $ u_{mu}$ and $ u_{tau}$ sectors, respectively. We look forward to the next-generation neutrino oscillation experiments textit{such as} DUNE, T2HK, and JUNO, especially the precise measurements on $ u_tau$ oscillations, to significantly improve the precision of unitarity test on the $3 u$ mixing matrix.
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