The travel-time calculation and characteristic analysis for first arrival in the 3D complex loess plateau area are of great significance to the analysis of the kinematic characteristics for seismic waves, the design of the seismic acquisition system, especially the first arrival picking and tomography inversion. To solve this problem: Firstly, the partition local variable density and unequal distance grid is adopted to divide the velocity model of 3D complex loess plateau; Then, a local travel-time algorithm of bilinear interpolation is established based on Fermat principle and upwind scheme and a modified group marching method is adopted as the scheme of wave-front expansion; Finally, the accuracy and efficiency of the algorithm and the characteristics of first arrival travel-time in the 3D complex loess plateau area are investigated by using the theoretical model. The results show that: We can greatly reduce the computational error caused by the singularity of the source and adapt to the complex seismic geological conditions of the 3D complex loess plateau unconditional stably and flexibly by using the scheme of variable density grid; Compared with the 3D layered uniform model, the travel-time field and time distance curve of seismic first arrival in 3D complex loess plateau area are more complex.