A finite-time suboptimal control strategy named $$$ \theta -D $$$ technique is proposed for the control of a class of control-affine nonlinear dynamic systems in this study. The nonlinear dynamic is expressed as a pseudo-linear form without linearization. By adding vanishing perturbation terms into the quadratic cost functional and using a power series to represent the co-state, an approximate solution to the Hamilton–Jacobi–Bellman (HJB) equation can be obtained through solving a differential Riccati equation offline and a series of linear Lyapunov equations with analytical solutions. The obtained suboptimal controller is in a state feedback closed-form. By tuning the parameters in the perturbation terms, semi-global stability can be guaranteed. In contrast to the finite-time state-dependent Riccati equation technique, the proposed method does not need intensive and iterative numerical computations, which facilitates real-time implementation. Two examples are utilized to demonstrate the effectiveness and efficiency of this proposed technique.