Thermal shifts of sub-levels R1 and R2 in YA1O3:Nd3+ has been measured. The behavious of the principal value of the integral in the single-phonon term have been investigated and the contribution of optical frequency branch to thermal shifts of sub-levels has been considered.By using the formulas involving Raman term, single-phonon term and term of optical frequency branch, thermal shifts of sub-levels R1 and R2 are calculated. Satisfactory agreement between the results of the theory and experimental values is obtained.