Abstract: The organic semiconductor poly(3-hexylthiophene) (P3HT) film prepared by the spin-coating method is optimized by dichlorobenzene (o-DCB) solvent added with chloroform (CF). The organic electrochemical transistor (OECT) is obtained using the optimized P3HT film as the channel layer and ion gel as the electrolyte layer. The effect of CF on the roughness and molecular order of P3HT film is inverstigated by atomic force microscopy, UV-visible spectroscopy and Raman spectroscopy. The effect of CF optimization on the electrical properties of the material is studied with a semiconductor parametric analyzer. Results show that CF introduction reduces the roughness of P3HT film and improves the order degree of P3HT molecular arrangement. The CF-optimized OECT exhibits significant synaptic excitatory pulse current characteristics under the stimulation of −0.5 V and −1.0 V electric pulses. Compared to the device without CF optimization, the amplitude of conductance regulation is increased by about twice and 16 times, respectively, along with the improved retention performance. The simulation results show that the accuracy of the neural network based on the CF-optimized OECT in recognizing MNIST（Modified National Institute of Standards and Technology） handwritten digits is increased from 73.6% to 92.7%. This device is expected to play an important role in large-scale neuromorphic computing applications.