Commonly used laser encoders are of non-common-path configuration. The non-common-path configuration between the measurement and reference beams is susceptible to environmental disturbances, and thus produces additional error. Under normal circumstances, the precision measurement, positioning process, and displacement measurement resolution and accuracy is greatly affected. Environmental disturbance factors make laser optical device technology. This study proposes a Non-focused Common-path Laser Rotary Encoder device called (NFCPLRE). NFCPRLE can effectively overcome the problems in the past without focused laser design. NFCPLRE compared with CPLRE for the grating quality requirements is also much low. In this study, NFCPLRE conduct experimental evaluation of performance test and error analysis with Renishaw Tonic interferometer for offset evaluation, it is displayed in the analysis and the experimental results. In the angular displacement of 360 degree, the average differential of NFCPLRE was 0.00149 degree with Renishaw Tonic interferometer. The time dependent drift of NFCPLRE was measured for a period of three hour and was found to be 0.00067 ± 0.0002 deg with 0.00014 ± 0.00007 deg resolution. It is therefore shown that NFCPLRE has enormous potential forfuture development.