Acoustic resolution photoacoustic microscopy (ARPAM) is a promising imaging tool in biomedical applications for its advantage of penetration over other optical imaging techniques. However, the lateral resolution of ARPAM deteriorates significantly in the out-of-focus region. The synthetic aperture focusing technique (SAFT) is required to restore this kind of focus-related imaging distortion. The conventional SAFT method is based on the virtual detector (VD) conception, in which the phase of the received photoacoustic (PA) signal is calculated by assuming the focus of the transducer as a VD. Nevertheless, the phase of the received PA signal is not only determined by the geometrical parameters of the transducer, but also by the transducer's electromechanic response and the original PA signal. Ignoring these two factors will reduce the quality of the imaging results. In this work, a new SAFT method, which is based on acoustic simulation, is proposed for ARPAM. The measured PA signal from a point target at the focus is employed to evaluate the convolution of the transducer's electromechanic response and the original PA signal. This measured signal is used as the excitation in an acoustic simulation. The simulation, which is based on the geometrical and acoustic parameters of the transducer, is employed to calculate the delay time and weighted coefficient for the SAFT calculation. The phantom experiments with point and line targets indicate that the proposed method obtains imaging results with better lateral resolution and improved signal-noise ratio compared with the widely used VD-based SAFT method.