Plant photosynthetic rate prediction models have the potential to enhance production efficiency and advance intelligent control in protected agriculture. However, due to the complexity of and variability in multiple environmental factors, conventional prediction models often fail to accurately predict photosynthetic rates. We hypothesize that the prediction accuracy of a photosynthetic rate model for cucumber could be significantly improved through the application of machine learning algorithms, including support vector regression (SVR), backpropagation (BP), neural network, random forest (RF), and radial basis function (RBF) neural network. To test this hypothesis, we designed experimental treatments with varying combinations of temperature, light intensity, and CO₂ concentration and measured the photosynthetic rate (Pn) during the peak fruiting period to construct a comprehensive dataset; we then determined optimal hyperparameters for each algorithm and established and verified four prediction models, thereby identifying the optimal model. The results showed that the maximum Pn value occurred at 28 °C, 1500 µmol m⁻² s⁻¹, and 1200 µmol mol⁻¹. Among all models, the SVR model exhibited superior performance on the test set, with an R² of 0.9941 and an RMSE of 0.7802 µmol m⁻² s⁻¹. This was further demonstrated by its performance on the validation set, where it achieved the highest R² (0.96443) and the lowest errors. In conclusion, the SVR model accurately predicted the cucumber photosynthetic rate, providing a solid theoretical foundation for intelligent environmental control in protected cucumber production.