as long as your REP(re-entry permit) is valid, you will not lose your PR status.
(A SPR will lose his/her SPR status if he/she leaves/remains outside Singapore without a valid REP)

for your case, what you have to do is to renew your REP, you can renew your REP at any Singapore Overseas Mission through your local representative or by post to Immigration & Checkpoints Authority.

P.S. All successful applicants must return to Singapore to collect their REPs.

and the documents needed to renew REP:

1. A letter (issued not more than one month ago) from the employer addressed to the Controller of Immigration, stating the date of employment, position held and monthly salary;
2. A statement from the CPF Board showing the CPF Contribution History for the last 12 months;
3. Income Tax Notices of Assessment for the last 3 years.

therefore

>>>PR要到期乐,能在国外renew 吗?本人现在不在新加坡, 短期内也回不来.是否可以在新加坡的当地大使馆办理哪
you can try to renew it while you are oversea, but you have to return to Singapore to collect your REP

>>>如果当时没有工作也可以renew嘛?
I dont think so

If you are self-employed (e.g. company director, sole proprietor, business partner),the documents needed to renew REP:

1. A valid Practising Certificate (this is applicable to applicants whose occupations require the application of such certificates before they can proceed with their respective professional practices in Singapore e.g. doctors, lawyers, etc); or
2. A valid Vocational Licence; or
3. A valid Business Registration Certificate (showing the names of all the Directors and partners) from the Instant Information Service, Accounting & Corporate Regulatory Authority (ACRA). You may wish to visit ACRA's website at http://www.acra.gov.sg or call them at 63253731 / 63253732 / 62486028 for further information; and
4. Income Tax Notice of Assessment for the last 3 years.

Note: An overseas application should be submitted at least 2 months before the expiry of the current REP. This is to allow sufficient time for processing. An overseas applicant whose spouse is a SC or SPR should furnish his/her spouse's Singapore identity card number and a copy of their marriage certificate to expedite processing. All successful applicants must return to Singapore to collect their REPs. A SPR who remains outside Singapore without a valid REP will lose his/her SPR status.