Abstract: In order to exactly simulate the rule of greenhouse cucumber Photosynthesis under different photosynthetic photo flux density (PPFD), a model named quasi-chi-square model (QCSM), was established. Net photosynthetic rate ( ) data of cucumber leaf were measured by Li-6400 Portable Photosynthesis System under dynamic conditions of temperature being 16, 20, 24, 26, 28, 30℃, respectively, and PPFD being 0～2000 μmol/(m2?s), and based on the measured values of , parameters of QCSM were fitted. The results showed that the estimated net photosynthetic rate data of by the model were coincided with the measured data of . Validation by yesteryear data indicated that model precision was very high with goodness of simulation of 0.9908 and residual standard error (RSE) of 0.4447. The estimated values of by QCSM were closer to measured values compared with that of minus exponential model (ME), and five parameter values of photosynthesis, including light saturation point (LSP), light compensation point (LCP), maximum net photosynthetic rate ( ), dark respiration rate (DDR), apparent quanta effect (AQE), were obtained. Compared with those by non-rectangular model (NRH), the estimated values of LSP, LCP and DDR by QCSM are closer to measured values.