Photoacoustic imaging is an emerging imaging technique that combines light illumination and ultrasound detection. Conventional design of photoacoustic probe usually combines light and sound in a straightforward way without any adjustable capability. In this paper, we propose a new photoacoustic imaging system based on light-adjustable handheld probe. Compared with traditional design of photoacoustic probe, our proposed apparatus has the following advantages: (1) Spot size and distance are adjustable. By tuning parameters, it can achieve bright-field, dark-field, and mixed-field light illumination schemes. (2) Different excitation modes can be selected as needed. Monte Carlo simulation results show that distinct light fields have different excitation advantages for optimizing photoacoustic generation. Both simulation and experimental testing results demonstrate the proposed system to have great potential in biomedical imaging with versatile configurations.