Abstract: Taking salt tolerant processing tomato strain KT-7 as test material, the pot culture method was used to study the effects of foliar spraying of hemin and zinc protoporphyrin（ZnPPIX） on the growth parameters, photosynthetic capacity, protective enzyme activity, and permeability regulating substances of processing tomato seedlings under NaCl stress(100 mmol · L^-1),in order to provide reference for alleviating the damage caused by NaCl stress on processing tomatoes.The results showed that compared with NaCl treatment, exogenous hemin could alleviate the damage caused by salt stress on processing tomato seedlings.Among them, applying hemin alone increased the growth indicators, photosynthetic pigment content, photosynthetic parameters, K⁺content, K⁺/Na⁺,osmotic regulating substance content, protective enzyme activity of processing tomato seedlings, and reduced Na⁺ content, relative conductivity injury rate, and malondialdehyde（MDA） content.After the application of inhibitors ZnPPIX（ZnPPIX and ZnPPIX+hemin） to inhibit the activity of heme oxygenase 1（HO-1）,the alleviating effect of hemin was limited.In summary, hemin could improve the photosynthetic capacity of tomatoes, enhance the activity of protective enzymes, reduce membrane lipid peroxidation, increase the content of osmotic regulating substances, and thus improve the salt tolerance of processed tomatoes.This alleviating effect might be positively correlated with the activity of HO-1.