Aim To develop and psychometrically test the distress thermometer for caregivers (DT-C) and document the distress level in primary caregivers of children and adolescents diagnosed with schizophrenia. Design A validation diagnostic accuracy study and descriptive cross-sectional survey. Methods DT-C was adopted based on Harverman's distress thermometer for parents. The cut-off score was detected by using receiver operating characteristic analysis with the Depression Anxiety Stress Scale-21 as a reference standard in a sample of 324 caregivers of children and adolescents diagnosed with schizophrenia in China collected between Jan 2017 and Feb 2018. Results One-item DT of DT-C indicated a good retest reliability (r = 0.86) and one-item DT and the Problem List (PL) indicated good convergent validity (r = 0.67-0.88). Overall and individual PL domains showed good internal consistency (KR 20 values ranged from 0.70-0.90). Setting seven as the cut-off score, the values of sensitivity (0.72-0.81), specificity (0.86-0.90), Youden's index (0.61-0.70), positive predictive value (0.67-0.74), and negative predictive value (0.84-0.92) were most satisfactory and area under curve values showed significantly excellent discrimination (0.88-0.90). The average DT score for the 324 participants was 6.34 (SD 2.49), with 46.9% of the participants above the cut-off. Caregivers above the cut-off score faced significant multiple problems in practical, family/social, cognitive, emotional, and parenting domains. Conclusion The DT-C, with six domains containing 35 items in Problem List and with the cut-off score at seven, can be a rapid screening tool to measure distress in these caregivers. The level of distress in caregivers was relatively high. Psychoeducation on specific needs and a solid mutual support network are recommended for mitigating caregivers' distress. Impact This study adapted a reliable DT-C to measure distress of caregivers, which has the potential to be introduced to caregivers of other types of child and adolescent mental disorders in research, assessments and care planning for health professionals.