Inclusion Criteria:  Volunteer to participate in this clinical study and sign the ICF before the study begins; Male or female patients aged > or = 18 years .  Patients with physician diagnosed Interstitial Lung Disease (ILD) who fulfil at least one of the following criteria for Progressive Fibrosing Interstitial Lung Disease (PF-ILD) within 24 months of screening visit despite treatment with unapproved medications(Unapproved medications used in the clinical practice to treat ILD include but are not limited to corticosteroid, azathioprine, mycophenolate mofetil (MMF), n-acetylcysteine (NAC), rituximab, cyclophosphamide, cyclosporine, tacrolimus) used in clinical practice to treat ILD, as assessed by the investigator:  Clinically significant decline in Forced Vital Capacity (FVC) % pred based on a relative decline of >=10%; Marginal decline in FVC % pred based on a relative decline of .> or =5 combined with decline in Carbon Monoxide Diffusion Capacity (DLCO) corrected for Haemoglobin (Hb) > or = 15% . Marginal decline in FVC % pred based on a relative decline of .> or =5 combined with worsening of respiratory symptoms Marginal decline in FVC % pred based on a relative decline of > or =5 combined with increasing extent of fibrotic changes on chest imaging Worsening of respiratory symptoms as well as increasing extent of fibrotic changes on chest imaging Note: Changes attributable to comorbidities e.g. infection, heart failure must be excluded. Fibrosing lung disease on HRCT, defined as reticular abnormality with traction bronchiectasis with or without honeycombing, with disease extent of >10% as confirmed by central readers. For patients with underlying Connective Tissue Disease (CTD): stable CTD as defined by no initiation of new therapy or withdrawal of therapy for CTD within 6 weeks prior to screening period. FEV1/FVC>or=0.7 before using bronchodilators. FVC > or = 45% predicted . Carbon Monoxide Diffusion Capacity (DLCO) corrected for Haemoglobin (Hb) > or = 30% and <80% predicted of normal. Female or male subjects agreed and promised to use effective contraception . Subjects are willing and able to comply with the protocol requirements and attend the visit assessed by investigators.  Exclusion Criteria:  Diagnosis of Idiopathic Pulmonary Fibrosis (IPF). Lung with other clinically significant abnormalities which investigator assess to have an effect on the results of study.  Significant Pulmonary Arterial Hypertension (PAH) defined by any of the following:  Previous clinical or echocardiographic evidence of significant right heart failure History of right heart catheterization showing a cardiac index <= 2 l/min/m² PAH requiring parenteral therapy with epoprostenol/treprostinil.  Major extrapulmonary physiological restriction (e.g. chest wall abnormality, large pleural effusion) Expected to receive lung transplantation during the study. Expected survival is less than 6 months. History of tumors within 5 years before screening (except for localized cancers such as basal cell carcinoma) Thyroid dysfunction that the investigator assessed to be clinically significant and needed to be treated.  History of unstable or worsening heart disease during the 6 months prior to screening, including but not limited to the following:  Myocardial infarction ; Unstable cardiac angina ; Congestive heart failure (need to be treated in hospital or NYHA III/IV); Uncontrolled severe arrhythmias. TBIL >1.2 × ULN ； AST or ALT > 1.5 × ULN. CLcr<60ml/min Human immunodeficiency virus (HIV) antibody is positive. Uncontrolled hepatitis B virus infection or hepatitis C virus infection.  Use of any of the following medications for the treatment of Interstitial Lung Disease (ILD):  Strong inducers or strong CYP3A4 inhibitors within 4 weeks before randomization; Azathioprine (AZA), cyclosporine, MMF, tacrolimus, oral corticosteroids (OCS) >20mg/day and the combination of OCS+AZA+NAC within 4 weeks before randomization; Cyclophosphamide within 8 weeks before randomization; Pirfenidone or nintedanib within 3 months before randomization,or have a history of continuous treatment with pirfenidone or nidanib for ≥3 months; Rituximab within the 6 months before randomization. Subjects canot complete the PFT、6MWT,or questionaires. Allergic to any component of HEC585 Tablets or pirfenidone tablets. Participated in other clinical study and received the last dose within 3 months before screening. Pregnant or breastfeeding. History of smoking within 3 months before screening or are unwilling to quit smoking during the study. History of alcohol or drug abuse within 6 months before the screening; Any condition that, in the opinion of the investigator, would compromise the safety or compliance of the subject, or prevent the subject from completing the study.