It is an effective way combining optical interference technology with astronomical telescope technology to raise the astronomical observation resolution. We use a telescope array to replace the large-diameter telescope for light-gathering observation. The maximum baseline is equivalent to the largest diameter of traditional optical telescope. To a great extent, it solves the problem of single telescope, whose light-gathering ability is not sufficient and angular resolution is not so high. In practice, only if the requirements below are fulfilled can the two beams be partly coherent: the phase difference must be relatively stabilized; it exists the component of mutual parallel oscillation; it has the same frequency; the oscillation amplitude difference of the two beams which vibrate at the meeting point is not so large and the optical path difference (OPD) of the two beams at the meeting point is less than the coherent length and so on. The sub-telescope should be mutual interference. Two parallel beams interference and OPD requirement formula are deduced. We get the requirement of the two parallel beams and the OPD based on the research on the two-beam parallel requirement and the OPD. Two indexes for the OAS telescope sub-telescope beam parallel and OPD are got combined with the OAS telescope character. The method of two beams interference parallel and OPD adjustment is introduced. The adjustment method for parallel and OPD optical system is researched which fits with the OAS telescope. The improvement for the system is discussed in the end.