The principle of legality of judicial expertise means that judicial expertise activities must strictly abide by the provisions of national laws and regulations. It is the premise to judge whether the appraisal process and results are legal and whether the appraisal conclusion has the effect of evidence.

This principle is mainly reflected in the process of legislation and evaluation:

1, the identification subject is legal.

2. The identification materials are legal.

3. The appraisal procedure is legal.

4 identification steps, methods and standards are legal.

5. Five aspects of the legitimacy of appraisal results.

1. The judicial authentication institution must be a legal authentication institution that has obtained the right to execute judicial authentication according to the provisions of laws, regulations and departmental rules, or a specific authentication institution entrusted according to the prescribed procedures. The judicial appraiser must be a natural person who meets the prescribed conditions and has obtained the professional qualification license of the judicial appraiser.

2. Judicial authentication materials mainly refer to the objects of authentication and the samples (samples) to be compared. The object of appraisal must be the special problem in the case stipulated by law, and the special problem not stipulated by law cannot be used as the object of judicial appraisal. For example, at present, China's judicial psychological measurement (commonly known as polygraph) and odor identification (police dog identification) are not legal identification objects, and their identification conclusions cannot be used as evidence. Moreover, identify the source of materials (including extraction, preservation, transportation, supervision, etc. ) must comply with the requirements of relevant laws and regulations.

3. The legality of the identification procedures in the submission, decision and entrustment, acceptance, implementation, supplementary identification, re-identification and expert identification of judicial expertise must comply with the provisions of the procedural law and other relevant laws, regulations and departmental rules.

4. The steps and methods of appraisal shall be confirmed to be effective according to law, and the appraisal standards shall conform to the national statutory standards or departmental (industry) standards.

5, the legitimacy of the appraisal results, mainly for the legitimacy of the judicial authentication documents. The appraisal document must have the document format and necessary contents stipulated by law, and the appraisal conclusion must meet the evidence requirements and legal norms.