Spectroscopy is an effective method in analyzing structure、 component and content of substances due to its high sensitivity. It can diagnose diseases in level of molecule and cell from the changes of tissues、 body fluid and cells. Compared to other methods, It has non-destructive、 non-invading and high-automatization in medicinal diagnosis. In addition, it may be used as a potential tool for diagnosing cancer in early stage.Spectroscopy has an evident advantage in componential analysis and cancerous diagnosis. But at present many groups in domestic and overseas mostly focus on the spectrum research in one sample of some illness, not in some samples of more illness to find their distinctness. This thesis applies itself to research absorption spectrum of the malignant plasma in oesophagus、 osteoma and leukaemia, meanwhile it has applied spectroscopy to measure the normal、 hyperplastic、 malignant mammary samples of albino rat which DMBA was injected into.This thesis includes two parts and some important conclusions are drawn:In the first part, this thesis has analysed absorption spectrum of the malignant plasma in oesophagus、 osteoma and leukaemia. The research arrives: We can diagnose the three diseases on the grounds of the ratio (I279/I253) of peak and bottom value in their absorption spectrum of plasma or the ratio (A_(414)/A_(282)) of relative componential content which data of their absorption spectrum of plasma have transacted more well and truly. And the veracity (about 79. 2%) of the ratio of peak and bottom value is higher than it (about 75.8%) of the ratio of relative componential content which data of their absorption spectrum of plasma have transacted. These parameters can provide some references and gist for doctor quickly