The d-invariant is a powerful invariant of 3-manifolds which is useful in answering a number of important problems in low-dimensional topology and knot theory. Mostly the computation of the d-invariant can be done by using purely combinatorial methods. In this talk, I will describe the calculation procedure of d-invariants of almost simple linear graphs which is based on the simplification of the original Ozsváth-Szabó method. This is a joint work with Çağrı Karakurt.