In order to improve the sustainability of Urban Employees’Pension System，some schol- ars suggest that it’s useful to improve the financial situation of pension fund effectively by adjusting the contributory service policy ( e． g．by increasing the minimum vesting period or mandatory retirement age) ．Based on the system，this paper builds the actuarial model from pay-as-you-go and funded fi- nance perspective，to analyze the effect of the contribution service policy adjusting on the sustainability of the system through the “contribution period”variable．The result shows that，average employee should contribute for more than 20 years to keep the horizontal balance of the pension fund under the frame of the current system．Moreover，it’s difficult to improve the financial situation of pension fund ef- fectively even if we lengthen the minimum vesting period or raise the mandatory retirement age．The conclusion shows that State Council Document 38 in 2015 decreases the effect of increasing the contribu- tory period on the system sustainability．Therefore，the expected effect of increasing the mandatory re- tirement age should be re-examined．The paper suggests that we should insist the principle of actuarial balance and take comprehensive measures to build a fair and sustainable system．