The matching of Z-increment and single cladding layer height is a key factor for improving cladding quality of thin-walled parts, so arc-section inclined thin-walled parts are formed by laser cladding forming with variable Z-increments. Under three-axis and open-loop control, the relationship curve between offset and Z-increment is obtained by laser cladding vertical and inclined thin parts. The result shows that Z-increment decreases gradually with offset increasing and when the offset ΔX is between 0.06 and 0.08 mm, the Z-increment ΔZ reaches its maximum decreasing rate. The biggest slope angle of deposited inclined thin parts is 36.6°. The offsets and Z-increments at the quinquesection points calculated by the relationship curve compose two-dimensional arrays. The optimized cross-section path is simulated by filtering and combining the arrays in accordance with the arc shape through Matlab program. Using the arrays of offsets and Z-increments obtained, arc-section inclined thin-walled parts with 136 layers are formed, and the dimension error of cladding height is under 0.78 mm, which is in agreement with the simulation and demonstrates the feasibility of forming arc-section inclined thin-walled parts with the method of variable Z-increments.