The performance of proportional plus integral (PI) and proportional plus integral plus derivative (PID) controllers are investigated, using a horizontal tank liquid level as the control object. Additionally, sliding mode controller (SMC) is designed and suggested for the level control of horizontal tank process. Also, the closed loop responses of PI, PID and SMC are analyzed in MATLAB and the response of the horizontal tank model are obtained in different set-point levels. This work presents a SMC approach that improves control accuracy, set-point tracking and robustness in level control of horizontal tank process, where traditional and existing PID controllers are less effective. These results demonstrate that the designed SMC controller markedly reduces settling time and also completely eliminate the peak overshoot compared with responses of PI and PID controllers, and similarly minimizes the values of integral of absolute error (IAE) and integral of squared error (ISE). These findings underscore that SMC provides superior performance compared to PI and PID controllers. Furthermore, SMC offers an improved closed loop performance of level control of non-linear horizontal tank process. It also provides more efficient and stable system responses.