In this paper, we theoretically investigated the influence of nonlocality on (1+2)-dimensional spatial solitons in undoped nematic liquid crystals (NLCs). We confirmed that the nonlinear index coefficient and the general characteristic length of the nonlinear nonlocality for the NLC are dependent on the pretilt angle of the NLC molecules. Then the Schrdinger-type nonlinear equation in strong nonlocality was given and from the equation the analytical expressions of the single soliton and the critical power were respectively obtained. In experiment, we varied the degree of nonlocality by changing the bias voltage and indirectly determined the relation between the critical power and pretilt angle. At last, by comparison of analytical solutions with the numerical simulation and the experimental result, we verified that our expressions are precise.