Solar sails, characterized by passive propulsion, have attracted an increasing attention of researchers, which has important value in the field of deep space exploration. SIASAIL-I is an on-orbit verification mission for solar sails based on a 6U cubesat, designed and produced by Shenyang Institute of Automation, Chinese Academy of Sciences (SIA, CAS). SIASAIL-I deployment mechanism is composed by two-stage deployment system, which can achieve direction transformation, stretching and membrane deploying in the narrow space of the cubesat. SIASAIL-I only takes up within 0.5U (48 mm × 90 mm × 95 mm) space and the total mass is within 1kg. SIASAIL-I was successfully launched from the Xiaoxiang-1 07 satellite on August 31, 2019, and successfully deployed a 0.78 m × 0.78 m sail in low earth orbit in December. This paper introduces the design process of SIASAIL-I system, including deployment mechanism, a series of ground experiments, and an de-orbit mission analysis, which aims to provide some engineering experience for the development of solar sails.