Seaweed Gracilariopsis lemaneiformis is mainly used as the bait for abalone and raw material for agar production in China. This macroalga is widely cultivated along the coasts of China from south to north, but its cultivation period is limited by high temperature in summer. In the current study, the effects of heat and phytohormone treatments on Rubisco large subunit (rbcL) and heat shock protein 70 (HSP70) were investigated by using quantitative real-time PCR and Western blot technologies in G. lemaneiformis. The results showed that transcript and protein levels of rbcL in G. lemaneiformis were inhibited by heat stress (33 ℃), however, 100 μmol/L salicylic acid (SA100) and 50 μmol/L methyl jasmonate (MJ50) treatments reduced the inhibition of high temperature on the expression of rbcL. In SA100 and MJ50 groups, the transcriptional expression of rbcL increased to 1.31- and 1.32-fold at 3 h, and the protein levels of rbcL were enhanced to 1.36- and 2.10-fold at 24 h compared to the heat-stress group, respectively. Moreover, SA100 and MJ50 effectively alleviated the inhibition effect of heat stress on Rubisco activity, and recovered the Rubisco activation states. However, the addition of 50 μmol/L abscisic acid (ABA50) mainly inhibited rbcL expression and Rubisco activity. Heat stress stimulated the transcript and protein levels of HSP70; hsp70 transcript expression further rose by 0.53–1.00 times at 3 h, and its protein expression enhanced by 0.93–2.45 times at 24 h in the heat-stress group after applying SA100, MJ50 or ABA50. In conclusion, SA, MJ and ABA play a certain role in regulating the inhibition of photosynthesis enzyme and the induction of heat shock proteins caused by heat stress.