Abstract: With the step or anti-step change of blue light-emitting diode on tomato leaf，the dynamic course of the photosynthetic parameters including photosynthetic rate（Pn），intercellular CO2 concentration （Ci），stomatal conductance（Gs）measured by using a CIRAS-2 of PP system and chlorophyll fluorescence deriving from 680 nm（F680）measured by using Fiber Optic Spectrometerinstrument（QE65000）were recorded and analyzed. When the intensity of blue light step rose，the dynamic process of rise-saturated trend for Pn，symmetrical trend for Ci as comparison with Pn，firstly decline then raise for Gs，as well as rapid increase for F680 from original stabilized state phases to new stabilized state phases were observed under each starting point or order point of light intensity. However，the opposite dynamic process for Pn，Gs，Ci and F680 were presented as comparison with step-rise of blue light under the intensity of blue lightanti-step reduced. With the increasing of strating point，the incrasing amplitude of Pn from original stabilized state phases to new stabilized statephases was gradually reduced under the same stepping quantum 200 μmol • m-2 • s-1. According to the above analysis，the results showed that insignificant effect of Gs on the dynamic process of Pn and diffuseness of CO2 into intercellular space，because the Gs was maintained at a high level with a slight decline for a short time after step rising of light intensity. The greater reduce of Ci owing to fast absorption and consumption by photosynthetic dark reaction remarkable impacted the dynamic course of Pn. And the actual light quantum yiled of PSⅡY(II)′ which calculated by dynamic changes of chlorophyll fluorescence F680 under unsaturated stimulate light show increasing trend of saturation with the increasing of light intensity step，this shows that the increasing of light intensity levels related to light electronic transfer rate provide more energy driving force for the regeneration of 1,5-ribulose bisphosphate（RuBP），so the Pn show a increasing trend from the original to the final steady state.

Key words: tomato, dynamic photosynthesis, light intensity step, chlorophyll fluorescence