Temperature-dependent Raman properties calibration and laser absorption evaluation are two significant sources of error in measurement of nm-thick materials thermal conductivity based on steady state Raman spectroscopy. A new Raman probing technique, frequency-domain energy transport state resolved Raman (FET-Raman), is developed to resolve these issues and improve the measurement precision significantly. The FET-Raman uses a steady-state laser and an amplitude-modulated square wave laser for heating the material and simultaneous exciting Raman signals. Under these two energy transport states, Raman-shift power coefficients for both states are determined, and their ratio is used to determine the in-plane thermal conductivity of nm-thick material. Four MoSe2 samples with different thicknesses (5-80 nm) suspended on a circular hole are used to explore the capability of this new technique. The in-plane thermal conductivity of these samples increases from 6.2 +/- 0.9 to 25.7 +/- 7.7 W.m(-1).K-1 with increased thickness. This is attributed to the increment of surface phonon scattering effect for thinner samples. The FET-Raman technique provides a novel way to measuring thermal conductivity of nm-thick materials with high accuracy and great ease of implementation. (C) 2019 Elsevier Ltd. All rights reserved.