Optical-resolution photoacoustic microscopy is a novel imaging technique that combines the advantages of optical and ultrasound imaging, enabling high-resolution visualization of biological tissues at the micrometer scale. However, the divergence of the excited Gaussian beam limits the depth-of-field of the system to less than 100 μm, which hinders accurate three-dimensional imaging of living tissues and restricts its applicability in biological research. Therefore, there is an urgent need for an effective method to enhance the depth-of-field without altering the hardware configuration. This paper presents a photoacoustic microscopy depth-of-field extension method and system based on three-dimensional continuity and sparsity deconvolution. This method utilizes a depth-varying point spread function and incorporates continuity and sparsity constraints into the deconvolution process to mitigate the effect of background noise, enhancing the stability and accuracy of the depth-of-field extension. Experimental results using tungsten wire phantoms suggest that the depth-of-field of system can be extended to 650 μm, which is 7.2 times greater than conventional system, while improving the resolution of the defocused region by an average factor of 3.5. Furthermore, experiments on zebrafish and nude mouse ears with irregular topologies demonstrate that the proposed method successfully overcomes image blurring and the loss of structural information due to limited depth-of-field. All the results suggest that the system with higher lateral resolution and enhanced depth-of-field has significant potential for a wide range of practical biomedical applications.