Sperm dark brown left testicular pain, clinical possible causes are orchitis, epididymitis, seminal vesiculitis and so on. 1. Orchitis: this disease refers to the inflammatory reaction process caused by the infection of testis or testis and epididymis by pathogenic microorganisms, common pathogenic microorganisms include bacteria, chlamydia, virus, mycoplasma and so on, which are usually associated with sexually transmitted infections, with clinical manifestations such as high fever, swollen and painful testicles, semen abnormality and so on. 2. Epididymitis: this disease refers to an inflammatory disease of the male reproductive system mainly characterized by swelling and pain in the epididymis, often coexisting with orchitis, mostly seen in young and middle-aged men with an active sex life, with clinical manifestations of unilateral pain and discomfort in the epididymis and swelling, accompanied or unaccompanied by fever, and in some cases, there are also urinary tract infections. 3. Spermatitis: this disease usually occurs simultaneously with prostatitis, mostly associated with retrograde infection, common causative organisms are hemolytic streptococcus, staphylococcus aureus and Escherichia coli, etc., the clinical manifestations of blood semen, perineum swelling, ejaculatory pain, etc.. If there is a relevant situation, it is recommended to go to the hospital as soon as possible for consultation and targeted treatment.